I'm in 100% agreement with Atmasphere. You will see many suggestions to use a cheater plug permanently to eliminate (mask) a ground loop problem. As Atmasphere suggested, use it only to identify the problem with the amp or pre-amp. After you have identified the problem, fix it. not by using the cheater plug permanently, but by actually fixing the problem. It could be a wiring problem in your house or a problem with a component. Sometimes it can be the interconnect cables. lifting the ground on a permanent basis is not a good idea. It is actually akin to removing your brake pads in your car. You don't need them until you have to apply the brakes. using a cheater plug removes the path to ground. If there is a fault, electricity will try to find another path to ground. It may be you, your pet, your family member, etc. I would bet that it is a problem in your amp or pre-amp that has come about recently. A faulty power supply filter cap or something else in the amp or pre-amp. If it was working fine before, maybe a dimmer switch is going bad. Some dimmer switches click off completely and some only turn down but not completely off. I know you will find the problem and resolve it.