I'm posting this looking for help from someone who knows class D amps really well. I design audio gear for a living (but haven't done work on class D amps), so feel free to get a bit technical if need be. I have one and only one gig where I need an amp, and it's a quiet gig - I have to keep up with an acoustic piano, and that's about it. I have a little 110 cabinet that I built that works great - puts out plenty for this application, and fits easily in my trunk. The trouble I'm having is with modulation noise (or something that sounds like modulation noise) - it's a little like a speaker buzz, but not quite - more white in spectrum than that, and it happens over a wider dynamic range than a speaker buzz, though there is harmonic content related to the original signal as well. I'm nowhere near clipping or the physical limits of the speaker when this happens. There is a bit of a whine when I'm not playing, but that's very quiet. When I play, the fuzzy, whitish noise moves up and down with the signal. I don't think the audience hears it much, especially when others are playing, but I certainly do, being right on axis of the speaker. I think it's a power issue - at home, I can't replicate it _ I have literally turned the speaker upside down, and on its side to make sure it's not in the speaker. I've used 3 different amps, and a couple different basses trying to get it to misbehave at home, but so far, no issues at home with that speaker or either of 2 amps. At the gig, I've had the issue with 2 different amps - a Fender Rumble head and a TC Eleectronics BH250 - both use class D amps (they might enven use the same power module, for all I know). There's a power "snake" that gets used at that venue - a long heavy cable, with taps every few feet. A couple powered monitors get plugged in in addition to my amp. Does this kind of behavior suggest anything to anyone who's got expertise in this area? Aged Horse?