I have a Roland KC-500 that makes random popping noises. It's a relatively low pitch, definitely a "pop" not a "crack" or "crackle". It happens every 1-4 minutes or so whether or not an instrument is plugged in. It is possible to initiate the pop by bumping the amp gently, though you can't get a 2nd pop immediately after the first; it seems to need a moment to recharge. The volume of the pop correlates to the level of the volume knobs.
Any suggestions for cause and cure?
Thanks!

If I had to guess, I'd say a cap is not soldered well or is defective, and as it charges, it eventually reaches the point where it arcs to ground (or the next component).. again instead of constantly connecting via proper soldering. If you don't know how to trace this sort of thing, you have 2 choices: take it to a tech, or learn to love pops and play only tunes that are in time with them .

Best, Paul

Thanks for your advice!