Off the wall suggestion. On the SWM system, each tuner is allocated a piece of the SWM dish-to-receiver frequency spectrum and this changes depending on how many tuners are active and which transponder they are looking at. If you have a problem that affects only the high frequencies in the SWM frequency band, you can possibly get this problem. At a different time, with different receivers "on", and different channels being tuned, the problem can seem to disappear. If that is the issue, it's nearly always a poor connection or cable fault.