I just purchased a 2006 xA and it has a module on the passenger side back of the roof. It looks like it might be a XM radio antenna.
The car does not have the original radio in it so I can't tell if that is what it is. It currently has a Kenwood that is XM ready.
It looks like it was factory installed.

Can anyone tell me what it is?

Thanks..

___

 

I know this is an old question, but no one answered. I can't tell you what it is, but you are probably right that it is an XM Antenna. However, I can say this was NOT a factory option. That had to have been installed after-market.

 

It is a Sirus Satellite Radio Antennae. The other part is located on the floor under the passenger seat I had removed mine
but it was bolted to a metal plate that is fixed the the carpet. I don't know if it's a service box, receiver or amp.
But it's stamped with a Sirus logo.

Mine was inside between the headliner.

____