I was recently given a jbl GTO 1020 sub because it makes noise at upper volume. I thought i'd just take it and see if there's anyway it can be fixed. I wired up the sub and it played fine at low volume but once it was turned up about half the sub started to make a noise similar to the sound your TV makes when you turn the VCR on when your not on channel 3. it only makes the noise when the sub does a hard hit or a situation with lots of excursion. also if you push on the sub (while it's off) with even pressure all around it does not amke the noise but if you push on it with one hand only on the right side of it, it makes the noise and feels like something is rubbing. What is wrong??? can it be fixed???