You seem to be gettting tired, lots of typo's.
Mine does it anytime it feels like it. It gradually comes in with a beebing hum becoming increasingly more annoying, like swarm of Canadian mosquitoes

, and then it dissipates. It will do it while I am watching something or when there isn't any source being fed to it (while it is still on, it has an auto shut off). And as I said before the KLH I had before did exactly the same thing with a completely different receiver.