Just overcame a similiar problem. It was a textbook receiver problem and ended up being the LNB's. No one and I mean no one, even one of the engineers at Hughes said it did not make sense it could be the LNB.
10 minutes later vuala no more problems. The system in question was had 3 receivers 2 of which were fine consistantly the 3rd would start chirping and eventually pixelize and then search for satelite signal. I replaced every possible component in the system from the box to the multiswitch, cable, interconnects, and finally the LNB that couldn't possibly be the problem.
Good luck,
CMack