I played my gig on Saturday at a place I have played about five or six times prior. I set up my amp, turned it on, and this horrible hum/crackle potruded from my speaker cabs. I am using a Demeter HBP-1, QSC PLX-1602 (bridged @ 4 ohms), 2ea Aggie GS112's, and a Lakland 55-94. I do not know what could make my amp hum/crackle so bad. I set my preamp volume at full open and adjust my master volume through my power amp. All of my cables are good. There were no neon signs lit. Out of the five or six times I have played there, this has only happened to me once. The funny thing is that we rehearsed for four hours prior to the gig and no weird sounds. I get to the gig and all this noise. After the gig I try my amp at home and no buzz. Help me! What was going on and how can I prevent this.