JBL sub issue

[Adam P]

I know this isn't really recording gear related, but I thought I might ask anyway.

I have a JBL PowerBass sub with a 10" speaker (150w I believe) for my modest home theater system. It's worked wonderfully for me since I bought it in 2002, until just a few days ago. The other day it started emitting a loud constant higher frequency (for a sub) sound. Unplugging the cable from my receiver didn't do anything. The noise is the same regardless of how the volume is set, but does change in tone when I switch between its dedicated LFE mode or normal mode with adjustable crossover. I've tried plugging it into several other outlets in my house and the results are the same as soon as I plug it in.

Anybody have any insight as to what the problem might be? Thanks.