There's no crossover in the 810e because they don't have tweeters and there's nothing to cross over. Have you checked the physical connections of the wiring on the rear panel? Sounds like something might have come loose from what you're telling me, but we'd need to know more. Does this happen at any volume or only when you crank it? How big is the power amp you're using and what are your settings? Trying to determine if you have a real problem or you're an amp slammer
BTW, you can always call Ampeg during normal west coast business hours.