Just got an '07 GT sedan with TPMS a few months ago. I bought the OEM sirius and placed the antenna on the dash right next to that sensor (I think it's a temp. sensor). Started having problems with the TPMS light. The service dept. had to call Mazda NA who said it was interference from the sirius antenna that was causing problems with the wireless TPMS sensors. They recommended moving the antenna, which I did, but still had the problem. Brought it back in, they finally flew in a japanese engineer with special equipment to re-program some of the software. Their final verdict was that the interference caused the software to get scrambled. It's also possible that the software got scrambled for some other reason, but the only way to test it out would be to put the antenna back on the dash.
The dealer and Mazda were very good about this, it cost them a substantial amount of time and cost to fix this. They could have said it was not covered under warranty because of unauthorized mods (the OEM installation instructions tell you to put the antenna on the trunk lid for the sedan), but they didn't. They said there are two wireless antennas for the TPMS, one under the dash in the center and another somewhere in between the rear wheels. They strongly recommended putting the antenna on the exterior.
If you have TPMS and are going to put in SAT radio, strongly consider putting the antenna on the outside. You don't want to run the risk of having this happen. Hope this avoids this problem for some others...