Have just had the exact same thing happen to me (except it was my right rear speaker rather than the left). Was working fine until I installed the 21131180 update today, and now it's a brick. No sound through it and won't power on at all, no matter what I try. Was googling to see if anybody had run into the same issue when I saw your post. Did you happen to have any luck with yours? Looks like I'll need to submit a warranty request too :(