I am not an electrician. NOT AT ALL. But I wonder if your power strip isn't acting as a ground when it's turned off but isn't when it's on. I too think at the very least that outlet has problems. I had problems with an outlet and my rig. I was able to get a better sound by finding an outlet on a different circuit in the house. I had an electrician look at the bad outlet (3 pronged) and he said it wasn't grounded properly and that was causing the problem.