Fixed a hum, still have a question

Any satelite dish or cable company connection to this system? If yes, then you need a baluns or isolation transformer to break the ground loop the safety grounds (required for lightning protection) create.

Most home theater retailers should be very familiar with the device you need as ground loops are a very common problem. Often referred to as a baluns (transformer) isolation transformer or ground breaker. Prices start reasonable at under $10 and go up. The device mounts easily to your 75 ohm signal line usually near your sat receiver (but can go any place AFTER the ground block connection). Don't mount the device between the dish and the ground block or you'll defeat the safety ground.

You will find much additional info within the forums if you try the search engine (try: hum or ground loop).