Do you have an antenna hooked up for the tuner and is it grounded? Try removing the antenna and listen for the hiss. The 970 does not have a grounded plug so maybe your have a ground loop somewhere in the system. If any of your gear has a 3 prong plug, pull the plug and try the system. Have you switched the bass management switch? Does it change the sound if you do? Also, make sure all of the rear panel connection points are clean and clear of any debris which could be shorting them out. With EVERYTHING disconnected from the 970, except the outputs to the 7500, is the noise there? Does the volume increase when you turn up the power? If so, call Outlaw. They have a lot of experience with ground loops and all sorts of other stuff. They will help you out.