Home theater subwoofer warning noise

[Zeppelin21]

Ok, one day my sub began crackling at LOW volume or lesser (quieter) bass noises. So thats odd enough. I eventually took the whole thing apart and IT SEEMS it was just something rattling. The noise was not present when the speaker was out of the box. Anyway (i guess) i fixed that problem. The new problem occured when i put it back together. Now there is a warning type noise when i plug it in. Wuueeerrp wuueeerrp wuueeerrp...
This happens connected to stereo or not. I was very careful not to touch anything besides the speaker wires. Please help it sounds like it wants to self destruct. Nothing like fixing one problem while causing another.

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[americanaudiophile]

Sounds like the amp is oscillating. The crackling sound you heard before could have been from the amp too.
If the sub is from a legit maker they may offer a reasonably priced replacement amp if it's out of warranty.