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Discussion Starter · #1 · (Edited)
My Subaru has been making a slight rattle (like marbles scrambling) under light acceleration for the last month. Brought it in thinking it was exhaust and heat shield but they didn’t notice anything. Going to be bringing it in soon. Any ideas ? See comment below for reddit video (apologies for low quality)
 

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I have the exact same symptom & sound...light acceleration, bag of marbles but does not sound like valves rattling...a little less clunky than valves I think...just noticed it after my 60K kilometers service ($700CDN !!) which included a fuel system cleaning. They wanted $70 to clean the intake pipe? I respectfully declined. Coincidence? I think not. Please post any findings as I am sure the dealer will say it's 'normal'. SMH.
 

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The almost universal answer to your question and evidence is... detonation. Although I get no sound from your video, the camera is pointing directly at the engine, further supporting detonation as the issue.

It is easy and cheap to test this hypothesis... just fill up with the highest octane available with the tank low and drive under the same conditions as when you heard the unwelcome noise. Give the ECU some miles and time to relearn its tables.

Let us know what you find. I'm sure whatever you find that eliminates the sound will be valuable to others.
 

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Discussion Starter · #5 ·
I have the exact same symptom & sound...light acceleration, bag of marbles but does not sound like valves rattling...a little less clunky than valves I think...just noticed it after my 60K kilometers service ($700CDN !!) which included a fuel system cleaning. They wanted $70 to clean the intake pipe? I respectfully declined. Coincidence? I think not. Please post any findings as I am sure the dealer will say it's 'normal'. SMH.
Go figure... been having problems with my dealer too. Service packages are money grabs. I’m hoping it’s not serious. Appointment later this week and will report back.
I have the exact same symptom & sound...light acceleration, bag of marbles but does not sound like valves rattling...a little less clunky than valves I think...just noticed it after my 60K kilometers service ($700CDN !!) which included a fuel system cleaning. They wanted $70 to clean the intake pipe? I respectfully declined. Coincidence? I think not. Please post any findings as I am sure the dealer will say it's 'normal'. SMH.
 

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Discussion Starter · #6 ·
The almost universal answer to your question and evidence is... detonation. Although I get no sound from your video, the camera is pointing directly at the engine, further supporting detonation as the issue.

It is easy and cheap to test this hypothesis... just fill up with the highest octane available with the tank low and drive under the same conditions as when you heard the unwelcome noise. Give the ECU some miles and time to relearn its tables.

Let us know what you find. I'm sure whatever you find that eliminates the sound will be valuable to others.
Could be. I’ve heard of this happening in modern subies. It only calls for 87 in the manual yet I’ve heard of dealers recommending higher than normal to prevent the sound. How ridiculous. Will report back.
 

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In defense of Subaru... this happens in all cars and always has. I ride with my windows partially open year round. I hear it all the time to cars around me. It boggles me... the car is loudly letting them know it needs higher octane and they’re oblivious. I figure, stupid or listening to their manuals. “Not my problem.”

And it’s not just a “sound.” Google ‘detonation in cars.’

It won’t go Boom right NOW, but it’s like taking low doses of a poison. It won’t work right and WILL reduce power and gas mileage. Plus down the road the car will not be well off.

The cars of today are fighting owner cost projections and federal (and world) regulations. They’re forced to design them this way. As intelligent owners it’s our job to see through this mumbo jumbo... in not just cars but everything. Use your head; listen to the facts not the propaganda... your car is the horse’s mouth.

I have always used a higher octane than “called for” unless it called for 93, and even then different brands work better than others. I never want to have detonation in the first place.

Preignition is another animal altogether. It will kill an engine in a heartbeat. But that’s largely in forced induction cars and you dont need to worry about that.
 

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Discussion Starter · #8 ·
Hi all,

So I just heard back from the dealer. They replaced the PCV valve for free under warranty but suggested a terraclean service to rid all of the carbon build up (which was causing the rattle) - this is done during C service under fuel injectors I believe. Anyways, they weren’t willing to put that cleaning service under warranty so I argued for a discounted rate of some kind... they originally quoted me $250 - yikes. It seems odd that this car would have carbon build up with only 38,000 km. I’m wondering if people were into something about using higher octane gas even if the manual only requires 87.
 

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Discussion Starter · #9 ·
Second update: drove vehicle home and still a rattle noise... looked at the bill and saw a recommendation to fill up with premium gas (3 tanks and see if the sound goes away). Let’s see how that goes.
 

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Second update: drove vehicle home and still a rattle noise... looked at the bill and saw a recommendation to fill up with premium gas (3 tanks and see if the sound goes away). Let’s see how that goes.

Hi,

Was your issue resolved? Hard to tell from your video but my car makes a similar noise but I would describe it as a chain pulling. The dealer has replaced the timing chain etc but still are hearing the noise after several repairs. Curious to see if your issue was resolved.

Thanks,
 

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Hi,

Was your issue resolved? Hard to tell from your video but my car makes a similar noise but I would describe it as a chain pulling. The dealer has replaced the timing chain etc but still are hearing the noise after several repairs. Curious to see if your issue was resolved.

Thanks,
I had this issue. Filled up with 91 and the noise went away. Decided to try 89 as well and the noise never came back. From now on, I will only fill up with 89 or higher.
 

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Sorry to revive this, but I seem to have a similar problem. Around 2000 to 3000 rpm it will rattle mostly in 3rd or 4th gear. Its extremely sporadic and I've had no luck with the dealership as it doesnt happen when they drive it.

Its getting to the point now where even I let off the throttle, I hear it rattle more as the engine brakes and revs drop.

If I do try a higher grade fuel, is it ok to start putting it in while I still have 87 fuel in my tank?

Thanks
 

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I have a CLANKING sound happening when I go a hill with low RPM intending to drop speed when coming to a stop sign. It sounds like crap. Rattling/clanking. Like pistons are slapping against metal or something. Very difficult to record the sound. Took it to the dealer and explained and wrote out the issue, they could not reproduce. Need to set up a camera outside to catch it.

It always sounds so bad I give it some gas to make it shut up. This is with CVT, base. Around 1-2krpm
 

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I have a CLANKING sound happening when I go a hill with low RPM intending to drop speed when coming to a stop sign. It sounds like crap. Rattling/clanking. Like pistons are slapping against metal or something. Very difficult to record the sound. Took it to the dealer and explained and wrote out the issue, they could not reproduce. Need to set up a camera outside to catch it.

It always sounds so bad I give it some gas to make it shut up. This is with CVT, base. Around 1-2krpm
I have the SAME issue. I’ve had two of the same year outback’s do this. Any fix?
 

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I have the SAME issue. I’ve had two of the same year outback’s do this. Any fix?
No :(

Let go of the gas or press gas more is my workaround, lol.
 

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I have a CLANKING sound happening when I go a hill with low RPM intending to drop speed when coming to a stop sign. It sounds like crap. Rattling/clanking. Like pistons are slapping against metal or something. Very difficult to record the sound. Took it to the dealer and explained and wrote out the issue, they could not reproduce. Need to set up a camera outside to catch it.

It always sounds so bad I give it some gas to make it shut up. This is with CVT, base. Around 1-2krpm
This sounds exactly like my issue too, except mine happens around 2 to 2.5 k rpm. Also, it's a 5 speed manual.. its so frustrating because as you said its near impossible to record it from inside the car, and I've taken it to the dealership so many times but of course it refuses to happen on those days
 

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This sounds exactly like my issue too, except mine happens around 2 to 2.5 k rpm. Also, it's a 5 speed manual.. its so frustrating because as you said its near impossible to record it from inside the car, and I've taken it to the dealership so many times but of course it refuses to happen on those days
What you are referring to is known as "ping", or pre-detonation. Cars used to do this a lot more, especially back in the 1970's (when every manufacturer was trying to run as lean as possible) before we had knock sensors in our cars. What's happening is that the spark is advanced just to the point of 'knocking', but is stopping just short of that. Since the 1980's, every car has some sort of electronic device which retards the timing at the onset of detonation, so the light pinging you hear is unlikely to cause any damage. Adding even a small amount of higher-octane gasoline to the tank should make it go away. It's more an annoyance than a problem.

For those who live in higher elevation, gasoline is often sold about 2 octane-digits lower, so people driving from, say, Denver to Dallas will often find their engine pinging if they left with a tank of 85 octane before descending to lower altitude.
 

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No :(

Let go of the gas or press gas more is my workaround, lol.
Adding Higher Octane Gas fixed it. After researching this problem (sounding like marbles at 1,500rpm) I have found that the engine is most likely filled with carbon deposits. When you add high octane fuel the sound should go away. Shell claims that they can clean 70% of carbon deposits in your engine after 2,500 miles of using their highest octane rating. I am not a mechanic, I just want my car to not sound like marbles. Maybe there’s a way to clean all carbon deposits without spending so much money on premium gas (93) but for now i’m just going to use 93 for 3,000 miles and then switch to regular and see if the sound comes back
 

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Adding Higher Octane Gas fixed it. After researching this problem (sounding like marbles at 1,500rpm) I have found that the engine is most likely filled with carbon deposits. When you add high octane fuel the sound should go away. Shell claims that they can clean 70% of carbon deposits in your engine after 2,500 miles of using their highest octane rating. I am not a mechanic, I just want my car to not sound like marbles. Maybe there’s a way to clean all carbon deposits without spending so much money on premium gas (93) but for now i’m just going to use 93 for 3,000 miles and then switch to regular and see if the sound comes back
I noticed it first when I barely had any mileage on the car, so that's not the answer. And there's no cleaning difference between high and low octane. If that's your intent a cheaper way is to run fuel additives with cleaners on every fillup (I use MMO or TC-W3), along with a top tier gas, and run seafoam through pcv valve. Adding a bunch of acetone is also a solution for cleaning. But I don't think that's going to do anything about the knock.
 
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