hey. my position is this :
i am running a car pc. the PSU is very noisy. (it has AC running on its +12, 5 etc rails).
my LCD, is powered by 12 and 5v , from the PSU, and it has allot of Huming (noise). the noise rises , when i rev the engine, so i guess it's AC produced by the alternator.
if i power the LCD from a completly diferent power source (Wall outlet), the noise is still there.
so, i guess it cant be a ground loop, correct??(or can it still be a ground loop between the signal wires??)
the reason i am asking, was becouse i am planing on buying an external USB graphics card, and completly cutting the 5v supply from the PC , and give 5v from a different PSU. and i want to see if i sould use an isolated DC-DC converter, or just a normal voltage regulator , with allot of filters would work...