I just had a phone conversation about the WRX deceleration noise (grinding when lifting off the throttle, it has been discussed extensively on the boards) with a service advisor at my dealer. The latest word is that Subaru is aware that this is a common problem, and is working on finding a solution. Until they get instructions from SOA on how to fix it, they told me to basically just deal with it. They say that it's not a safety issue, and that there was no need to worry that the defect would result in other parts getting damaged.
He didn't seem comfortable talking about possible causes, but he indicated that they managed to fix the noise on another car earlier, after many attempts. I mentioned the post of the guy (variac) saying:
What they ended up doing was replacing the clutch disc, pressure plate, flywheel and bolts. I just picked the car up today, and so far so good... no longer has the noise. The clutch parts they put in were somewhat redesigned, ..
He wasn't very clear in his response, but my understanding was that they also replaced the clutch disc, and possibly other parts. When I tried to pin him down on this being the likely cause, he said that they couldn't be sure that the noise wouldn't come back.
So my current guess is that we can hope for redesigned clutch parts that will solve the problem. I hope it won't take too long... The service advisor told me that he would be mentioning the issue to the local service rep each time he sees him.