I noticed that on my AD30VT a couple of times. It seems if the kids turn the fan on in the one bathroom, it will pop when they turn off the fan. That I can understand, but later when I turn the amp off, it will happen again. It only seems to happen when someone turns the fan on - strange.

I know someone here can explain it, but I would pay attention to see if anything out of the ordinary happens on those occasions it pops. The only thing I've been able to do is make sure I turn master volume and the other volume (does it have a name) all the way down before turning it off. It may still be popping, but at least I don't hear it.