I have a 2008 Sundance 3300SK that had a Coby DVD/FM surround system in it that went bad. I bought a Sony DAV-TZ140 to replace the receiver. Now I have a hiss from both the DVD and FM radio. I bought ...
There is a chance you may have some wires crossed a bit and causing a ground loop. Those can drive you crazy. Radio Shack used to sell ground loop isolators. Here is a link for the device that just might solve your issue.