I actually have thought I heard something akin to a faint cell phone ringing on a few occasions, only perhaps a bit more on the "musical" side than a straight ring. Maybe "chiming" would be a better description.
This is probably the closest you can come to a description, especially the word 'chiming'. And it's definitely the most distinct during live broadcasts.
Side note - the tech came out on Tuesday and agreed that he could hear it as well. He realigned my dish, checked my equipment, and asked me to check to see if I could still hear it. In order to test that out, we turned it to TBS for whatever baseball game was on at the time....still heard it. He turned Dolby Digital off on the receiver and that was no help either.