noise in picture on video system

I hve an interesting thing happening to an install i am working on.

I put four 15" flip down monitors in a tour bus conected to a JVC 7400 single din dvd player.  There are also 8 4x6's in the overhead compartment over the seats. There is no engine noise in the audio... however; the picture has a slight bit of interfearance that looks similar to water in the picture.  The louder i turn up the sound, the worse the interfearance gets.

I have changed out the headunits.  Changed out the cables. Tried different screens. Ran a new ground from the source unit and screens to the battery. No change.  Ran a new power sounce from the battery. Still no change.  I even tried a high power 12 amp noise filter on the constant power lead and ground. That di nothing either. I am getting a constant 13.6v and the source unit and the monitors.  When i turn off the source unit; there is no interfearance in the picture to any of the screens. And, i am also using a 4 way video signal booster that i have also changed out, 2 no avail.

I am starting to pull hair out of my head. Can anyone offer any ideas that maybe i havn't tried.

Tahnks in advance.

David