Thanks, I haven't checked under the hood yet but it almost sounds more like an electronic sound rather than a belt or something like that.
Hey,
I just wanted to stop in a share some info about this issue. I also saw Tony's post when I was trying to figure out this problem in my 2018 Impreza Premium (CVT) - built in November 2017. The noise as far as I can tell is coming from the A/C blower motor housing. I took off the glove compartment and played around with all of the A/C knobs and the sound was only correlated with the fan speed setting - A/C on/off, vent selection, and temperature did not change the noise in any way, but putting the fan speed on the bottom half of speed settings caused the noise and turning off the fan caused it to instantly stop (unclear if higher fan speed settings silenced the noise or just muffled it).
That all being said, for me the noise seems to happen on hotter/more humid days (it started in ~ early August). I brought it in to the dealer last week on what was the hottest/most humid day of the year here so far so that they could try and diagnose the problem while it was making noise, but for some reason it stopped making noise when I got to the dealer (of course!). Interestingly however, it has been completely noiseless since then (5 days now). The only reason I can think of for this is that I was running the fan on the highest setting all the way to the dealer on a very hot day (~ 100 F) - I typically run the fan at a lower speed setting since I do not like it too cold - and perhaps the continuous high fan speed usage caused something to finally seat properly or friction caused something that was slightly out of specification to heat up/rub down to be in specification.
Just wanted to share my experience with this problem - I will let you know if it starts again.
Cheers