Sounds like a hardware problem. Double check your connections, especially any that use mechanical connectors (crimps, plugs etc.) as they may be losing contact during thermal contraction. A little circuit board or contact cleaner and then a dab of conductive grease should do the trick.

I've got SIRIUS (which is now $10 a month) and only occassionally do I not have audio first thing in the morning, but it's due to scheduled channel updates which just take a minute or so.

So check those connections and look over your cradle too, they're may be something preventing it from seating properly or allowing it to vibrate loose.