Some call them ground loops, some a 60 cycle hums while others use the term mains hum. Whatever term you use to describe the annoyance, knowing how to trouble-shoot them is half (more really) the battle of eliminating them. A ground loop is a hum associated with audible oscillation at the frequency of the mains alternating current, i.e. your homes electrical service. In many cases group loops (hum) in audio systems usually originate from the cable feed and or the satellite television lead from the dish.
Ground loops are typically (oddly enough) a grounding issue. Often times it’s either a broken ground that results in a hum or an intact ground that introduces the hum directly. The quickest way to eliminate the satellite or cable is just to remove the satellite or cable connection from the system and listen for the hum. If the hum remains with the cable removed you’ll need to keep looking at other pieces of gear and or connections.
If removing the satellite or cable TV feed makes the hum go away you’ll want to try one of two things, first trace your cable tv (or satellite) line back to its entry point into the house. If the feed has a splitter check to see if its grounded, if so lift the ground and then go back inside and listen again. If the hums gone you’ll want to look into alternate ways to protect you A/V system than the ground provided by the cable company. On the other hand if you see that the cable (or sat) isn’t grounded before it comes into the house that may be the culprit. All in all troubleshooting these problems is a process of elimination and a bit of experimentation afterwards.