i have a hartke 3500 bass head,its in "like new" shape,taken care of,using new guitar cords,etc. here is my prob. when i use this amp to gig it buzz's terribly,i have tryed the ground lift on rear of amp(does nothing) i have tryed a ground lift plug ,(it helps some),whats whacked is when i play the amp at my house everything works great. i am assuming it might be the lights? buzzing coming back thru from PA system? has anyone had the same prob and found a way to fix it? or should i just live with it? thnx in advance..