i got 4 head rest tv . when the car key is at accesori position the screens look clear but when i turn the car on you can notice lines on the screen peopl call the hum lines. i checked my ground and ive done every thing to it.
check video connections, may need a video signal amplifier..... try that, they are online for about $25 plus shipping, if that doesnt work kill yourself lol
You have 4 monitors and they are all running of one source? That sounds like weak signal is the culprit and you need the above mentioned video monitor. I have 3 screens and used one and it worked like a dream