For some reason my rear left speaker rumbles. I tried hooking up diferent speakers to it and they rumble too. I have a amp hooked up to my components. the other speakers are fine. I noticed the problem ocassionally will go away for a day. (very weird)

 

since you have an amp.. I guess it could be bad... also, just one speaker rumbles right? not all of them? so it is probably not alt whine.... I would just say that from what you said, it sounds like it would be a problem with the source channel for that speaker location. Check your wiring as well, make sure the wire is not touching anything.

This is not my best area.. but from what I have read, those seem to be the best options...