Sirius Prius Radio Loss of Reception

Anyone have this problem with a Sirius Prius Radio installed in an 06 Prius? When I start the Sirius Prius radio it is fine for about 5 minutes and then loses a signal for about two minutes for no apparent reason, followed by a regained signal for the rest of the car trip (an hour or so). It is like the reception going under a bridge (loss of signal) but it lasts for about about 1-2 minutes and then no problem. Any suggestions as to what might be causing it? I've checked the antenna connection and it seems OK, and if there was a short, it would not come back so flawlessly as it does. This is really a head scratcher!