XM antenna?

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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by H3OH:
Hockey puck with an antenna on top?

</div></BLOCKQUOTE>

Yes.
The wart on the top right hand side is the XM antenna, and the little thingy sticking up is the cellular phone antenna for the OnStar system.
Most of these warts also incorporate the GPS antenna.
Reason it can't be incorporated into one antenna with the AM/FM is due to separation of the signals; and the different type of signals. Almost all vehicles which have cellular communications, XM (or Sirius) never incorporate into a standard AM/FM antenna. There might be one out there, but I have never seen one.
Older systems used a separate wart for XM and another wart for OnStar. Some put the GPS for OnStar in the windshield at the very top. All depends on the OnStar system basically.