bump for you.
I just started noticing a similar noise last night driving home and again this morning. Only occasionally.
It's a whir ( ocassional) that occurs only under very light throttle ( less than 0 boost) and it seems to come from the right rear. Especially noticeable at 60 - 65 MPH.
Based on other cars that i've owned it sounds very much like a differential noise but reading about all the problems with WRX wheel bearings, that's a possibility. I don't think a wheel bearing would change with load/unload the way a rear end noise does. And I think a wheel bearing is more of a grumble not so much a whirring sound.
I've got 34.5K miles and just started researching this. the noise is not nearly as loud as the rear end noise on my beater or on my Dad's old mercedes ( definitely rear end noises) but certainly concerns me at such a low mileage
Will have to get it up in the air put it in gear and listen, I guess.
G