I noticed this the other nite driving home. when listening to the radio when i turned on my rear defrost, i lost all signal on all stations. but when defrost is off, it works perfect. is this a known issue or problem, or do i actually have a short or something happening in my car? i do notice the rear defrost is very slow to work. but does work. im not blowing fuses or anything either

 

The antenna in these cars is in the rear window, since there really close(practically the same place) it causes and interference when the rear defroster is on. I didn't notice it much on my monte carlo, well not as much as it happens in my 300. But I don't listen to the radio to overly often so it was no big deal to me

 

I believe it's behind the passenger side, rear interior quarter panel trim is a module that is used for the rear defroster and the antenna. I've been trying to chase down a problem with my rear defroster and a problem I don't have but have read about is what you described. Chances are high the problem is that module.