My friends Ampeg B-3 combo has started acting up. We replaced the pots last night and that fixed a lot of the noise issues, but not all. It runs fine (slight background hiss) for a while, then 20 minutes later intermittently cuts out, and or gets real noisy generating its own booms, and crackles. Filter caps? On/Off switch dirty/intermittent? Any and all ideas welcome. This is a basement amp, never gets moved, just used almost daily.