Has this issue always been true since the system was installed, OR, is it a new problem that recently cropped up? What receivers do you have, what switches, what cabling, how long is the cabling. If you have more than one receiver, does the problem happen on ALL receivers, or only one, etc? We need to know what and how everything is set up to try to figure it out.
I would say it's a cabling issue of some sort. Even a pinched cable can cause issues like this. First thing I'd do is check all cable connections, and make sure they are screwed in tight. Do NOT use a wrench to over-tighten them though!
With more info about your system, we might be able to give better suggestions
