Shark fin aerials on ML

[Gucci]

I have a black disc the size of a 50p piece on the top of my ML at the rear. I've seen a few MLs (W163) with a small shark fin at the same place. Would this be a retro fit to improve FM reception (mine is dreadful - it picks up some stations at standtill, but on the move it hisses).

 

[BTB 500]

Shark fin is usually a GPS antenna AFAIK - nothing to do with FM.