AvFan's recommended test is definitely the place to start. I've had problems like this in my system that resulted simply from unruly cable management (power cords to close to speaker cables or analog interconnects), but other common causes have been dimmer switches, light fixtures, or appliances dumping "noise" back onto the house electrical service - often with no proximity to the home theater equipment.

Any system is at potential risk of this sort of problem, no matter whose equipment you use. As for the 7200, it's still potentially subject to this - the 7200 forum may simply not have much mention of it because there may be fewer 7200's sold than 7500's and 7700's.