I reccently got a 7.2 inch screen and wanted to test it in my car so I hooked the video output of a home dvd player to the screen and the audio output to the rca cable going to my amps that power my speakers, and plugged the dvd player to an ac outlet. I watched a movie and sound worked fine but when I plugged the rca's back into my stereo and turned it on there was no sound, and if i touch the rca cables to some metal they pop and I can hear a little bit of music but it turns off as soon as I turn the volume. What's wrong? Was there some kind of backfeed through the dvd player or what. Pleassssse help!