Mine is not fixed any more. It came off a few weeks ago and is dangling by the cable. No detrimental effects, though.
I've heard several suggestions for this...
I don't have sat nav, so it probably isn't that.
Phone aerial has been mentioned a few times (but the bluetooth is in the arm rest?).
I've also heard central locking receiver.
I’m not sure, but someone here will know.
As GIXXERUK said it is the integrated phone pick-up from the 'chequer-board' aerial at the top and middle of the screen. Serves non-bluetooth phones so old-hat really now but then that goes along with the retro tape deck in the Bose
Oh, and welcome to the forum Roger