So its coming from only one speaker, and sounds just like the buzz from a split, broken surround, or cone puncture, like a paper-like edge that's leaking, leaf stuck in a fan, etc. Its audible right on axis with the upper 15", and goes away if I hold down on the cone. I've looked over the whole cone, dust cover and surround and there are no splits or loose edges or anything. Doesn't matter where I hold the cone or apply pressure. Its only noticable at home, but not with a band or at practice, so its not very loud - it was making it two years ago when I bought it and hasn't changed. Just thought some wisdom here might help me identify it.