Sub-Woofer goes off with loud noise 2:30am, A/V unit off, and everyone was sleeping. Investigate - speaker was left on. I turned it off. When turned back on ,still hear loud noise and a boom when switch is put to off position. All connections were checked - still same problem. Why?

Does it have an auto on or is it in standby mode?

It is not uncommon to hear subs making noise when switched on/off.

Note: When turned on there is a constant loud noise until you turn it off - upon turning it off, you hear a loud boom. Got any ideas why this happens? Its got me...

Does the sub still work? If not, its probably a blown amp or speaker.