so... some extra info:
1)after all the noise is on both screens.
2)even if i connect the big LCD to house outlet, (no inverter in system) , the humming is the same..
3) with car turned off, (no alternator working) , still the same
4) the speakers, still do some noise some times, even with ground isolators
5) I have the motherboard chasis grounded as well (same spot as anything else). IF i try to power up with that ground removed, the big screen wont start (it turns off and then off). IF i turn on the pc with ground, screen works with noise..