sounds to me like the signal hitting your mixer is clipping causing distortion.

Sounds like you need an exorcism to rid your subwoofer of the Oompah-Loompahs which may be living in there.

j/k, it sounds more like you may have a problem with the amp / speaker combo. Have you had the system tested? It may cost you a few bucks, but it'll save you hundreds if it fails on you.

Could be that you're overdriving the speaker to the point that the voice coil is bottoming out, making a popping sound.

Are we talking about really loud volumes, or normal volumes?

hrmmm ok now it sounds like a grounding/interference issue, make sure your audio leads and power leads dont cross each other or come into contact with each other.............

well i dont think it could be the amp clipping....since when QSC's do they shut off totally for about 2 seconds. as for grounding...the ground wire is the 3rd little cylider-prong thingy at the end of ur power cord. so you shuold be using an outlet with that same female shape to it, not using an adapter to bypass it. also getting a power conditioner is also very important, as it will help keep all power at the same level and help reduce noise and interference in the line. and as shawn wiseley says...always lights on a separate circuit. if you can't afford a power conditioner for them, just plug ur lighting contoller and fogger through a good quality computer strip, and run that to a totally different circuit. also, good quality heavy, thick, sheilded power and sound cables are best as well. you also mentioned about your levels....does your mixer have an input level meter? if so, us that to fine tune your signal. imy djm3k's signal was soooo hot for the amp so i turned down the master attenuator in the back of the unit. finally, if all that fails, then it's probably something wrong with your speaker or amp.

>DJ Tony C

I agree, but the outlet used for fog and lights not only have to be on a differrent plug, but a differrent circuit.
I had the occasional pop one night and found to much dust in my amp causing short circuits once in a while. I cleaned out my amp (crest ca9) and the problem was gone.
You could also still be overdriving those speakers. thats when you get a square wave instead of a curved wave causing a poping sound.
This might help also. (hope so)
Dutch.