The hybrid's electronics behind the back seat generate a lot of electrical noise. To keep the radio from picking it up they moved the antenna from he rear window ( where it picked up all of it ) to the roof which shields 90% of it.

To hear the noise take an old transistor radio ( the cheap $5.00 type that walmart or kmart used to sell ) on am on a weak station in the back seat and drive around.

That is why.

 

Makes sense; thanks for the insight!