I'm not sure if this is the right forum to post this on but as it's a performance issue.... We play with the same set up most gigs, and we play often...2 to 3 times a week. We have our own PA through which we put 3 vocal mics, a drum mic, and the keyboard. Sometimes the sound is perfectly clear and we have no problems, and other times we get really weird buzzing. First it manifests itself through my bass amp (Gallien Krueger 700RBll through an SWR Goliath cab). I use Monster Cables and the best of everything I can find, and yet there's still the buzzing. Then it's starts coming through the foldback monitors and then finally it will start on the guitar amp (a vintage Fender Twin). It's very frustrating and we constantly try to reroute things, like not have more than one thing plugged into one input and not use too many extensions. This never happens when we rehearse and I think it may be a grounding issue in some of the venues we play, but none of us know the first thing about electricity other than the basics of safety. How would one go about testing the grounding of a venue, and apart from using a surge protector which we do, what is the best way to protect our equipment? An idiot's guide to electricity 101 would be very helpful!