Sounds like we have the same problem and it is a unit fault. I take it you are out of warranty but give sirius a call and see what they say, They did not question me at all-almost seemed like they new of the problem. I bought the unit from Visions electronics (Canada) and not thru sirius. They did not ask were I bought it from and when it was bought. If not sounds like Matt here is the man to talk too.
Just my 2 cents... can't hurt to try tho!