For grins I decided to open up a very old JBL DPS-10 subwoofer I had in the back room that started making rude noises when powered up many years ago, and I never got around to getting it fixed (I decided I wasn't all that fond of rattling windows during actions scenes, so it didn't seem like a high priority :-).
Upon unscrewing the back plate and pulling out the circuit board, I eventually noticed some brown fibrous material on several components. Paying even closer attention, I realized it appeared to have sprayed outward from a central location marked C6 on the circuit board.
Currently residing at C6 are the apparent remains of some kind of capacitor. A busted plastic base and a couple of fragments of plastic and wire, but no actual capacitor left. My extensive expertise in electronics tells me this is probably a clue :-).
Here are a few shots of the destruction. The first picture is also important because it shows me where the speaker wires were connected before I removed the circuitry to examine it closer.