I just purchased the B115 with the b200H head, set it to the 'classic bass sound' setting provided in the manual, and I'm getting some buzzing. The volume is at a moderate level and I've tried a couple of basses yet the buzz rears its head on certain notes, mostly mid range. It's sounds as if it's coming from the top left face of the cab, plus there's a rattle on the output panel on the back, which is kind of expected. Has anyone experienced this or been able to correct it?