screeching noise from my overhead DVD player during FM transmission

[matt6288]

I just installed a overhead DVD player in my 2005 ford five hundred, the install went ok I cannot use the rca output to my head unit because It is only a single zone head unit, tried to cut the RCA and use them as speaker wire that didn't work so I have to use the FM transmitter the DVD player comes with. The problem is there is a high screeching sound when the sound comes through the speakers not enginge noise just a steady screeching noise with the sound of the dvd. how can I fix this or any other ways to get audio from this thing