Fm transmitter not playing through rear speakers

[AC Question]

I have a fm transmitter that seems to be only playing audio through the front speakers of my car. However when i use the normal cd system or tune into a normal radio station all speakers are being occupied. Im wondering if there is problem with the fm transmitter or if it is only channeled through the front speaks(note: ive used two diff brands of fm transmitters and still this same result). Any help or knowledge would be appreciated, thnx in advance

 

[Oggy Shopov]

Does it do it on all of the frequencies that the transmitter supports?