I apologize for polluting this thread. Despite being a member since 2003, I still don't have 15 posts and can't reply to a PM I received requesting information on my HG15BG subwoofer problem.
This is for linger63. Please PM me again when you've read it so I delete this post from the thread.
Response to your PM:
That's exactly the sound. Sorry!
I don't know for sure that it's caps, but it's worth checking.
I dabble in electronics so I've got something called an ESR meter on the way. It will allow me to test the electrolytic capacitors without having to remove them from the circuit board. In my case, it's worth the price of the meter (about 70 bucks) because I'll use it on other projects. If all the caps are good and nothing else is apparently wrong, I'll probably just send it in. Easier and they provide a one year warranty on the repair.
If you have an electronics repair shop nearby, it would definitely be worth the time to take the sub to see if they can repair it. If it is a failing capacitor, they should be able to do it with no problem.