whining noise

i just hooked up a flip down tv and a dvd player in my truck and now i have this whining coming from my speakers what causes that

Thats just ground noise. It comes from bad grounds, cheap rca cables, cheap equipment or a cobination of all these. Its a pain in the ass to eliminate but try these home remedies...
1.Buy a ground loop isolator for the rca's.
2. make sure you have a bare metal,tight clean ground.
3.try grounding the outside "prongs" of the rca at the unit on the sound cables not the video