Recently I have been having signal problems with the xm in my car. I have a Z1 with the pioneer GEX-P920XM tuner. The problem is that sometimes I will have a signal and sometimes it will just drop off like i am going into a parking garage or something. I called xm and they are not having any signal problems and they also refreshed my signal. I have had the system for about a year and a half. Is it possible that my antenna has gone up?