[wejones]

If it is just the audio and not video, then it is NOT the LNB. I'd agree with the last post, ie that it is a switch failing. I too have had an A/V switch fail for audio only, in fact I've had 2 such switches fail. If there is no A/V switch in the system, then I'd suspect the receiver itself. I've also recently had a digital receiver have the audio go out. Actually it went out on only one of the 2 stereo channels.
Years ago I had an expensive communications radio, which seemed to lose sensitivity after being on for more than a half hour. I took the thing apart, and found a transistor that if I touched a cold piece of metal to, it would bring the thing back to full sensitivity, but then it would slowly fade away again, either due to slowly heating up or slowly collecting static charge or something. Never did get it fixed. I just use it for short periods of time. :-)