It sounds like the sound chip on your card is fried. Did you have a power spike or lightning storm at the time? Did you handle the card without a ground strap?
The problem already existed when I tried reseating the card. (I wasn’t wearing a strap, but did ground myself by touching the metal computer case to prevent ESD.)
The only other thing I can think of is blowing out dust with a can of compressed air. I think this was sometime before the problem started.