I had a Bose 6 cd indash model with xm. the xm worked fine. i had the dealer install a factory navigation unit. They installed an antenna for the nav gps and everything works perfect except i no longer have xm. it comes up on the unit as "no signal" present. the dealer is saying it's because their isn't an xm antenna in the drivers side mirror. i'm at a loss because the xm was working with the old radio "without an antenna" per the dealership. HELP!!