Stavs is on the money. My experience, most recently on a AC/DC Premium, is that the plug on the flipper end stop comes loose from the end stop bracket and buzzes when the flipper is held up. The quick fix is to re-anchor the plug with lock-tite red or just replace the end stop with a new one. Simple check is to take out the end stop and see if the plug spins = if it does, that's your problem. Grab the lock-tite. IMO every Stern should come with a tube.