seems like static

I have a Rogue Magnum 88/99 combo. At the start up of the amp right after the warm up click of the cicuit, there is a zzzzzz. Then during random moments, even with the volume all the way down. I hear what sounds like a static discharge coming from the right speaker. the static is random, sometimes for a split second, other times for a second or so. All all random times from 10 seconds to 30 apart. I have tried everything to figure this out. Any suggestions?
Thanks, Scott