Now there can be a number of things that can cause hums in a system, but the most common ground loop issue is from two or more components in a system that are different phases of the AC line and sharing a common ground. Your home has 220v coming from the pole to your panel. It is then split 110v to each side of your panel, but each side is 180 degrees out of phase. So if you have equipment that are plugged into different outlets and any of the AC outlets are from different phases, AND your sharing a common ground you will get a ground hum.
So you always want to have your equipment on the same phase, and that is important when running dedicated lines, and good idea to have 20 amp lines. Now if that is not possible or you don't want to go to that extent, you can simply lift grounds. I have done it for years, never ever heard of any issues, in fact many systems I have installed I lifted either all grounds or left just one connected typically the preamp. Other issues can be dimmer switches, unshielded interconnects, power cords running parallel to speaker cables, refrigerators or appliances on the same circuit, just to name a few.