2005, 300 factory radio with one cd - 4 speaker system, antenna in rear window.. in california.. for 2 years on hot days above 100 degrees radio looses reception, as car cools down it comes back...NOW on cold overcast days radio looses reception until weathergets clearor warms up. as the weather clears the reception gradually improves until reception is fine... radio head was checked while acting up and it is ok, it is from the radio back.. does this car have a antenna module or booser, if so could that be it...has anyone heard of this...any advice....HELP

 

I would try cleaning the rear window first. found that just being dirty can cause problems.