engine hum through radio

Have had engine hum through radio for some time. Had mechanic look at it and replaced radio with after market. No luck. Doesn't do it all the time. Putting up window (power), turning on lights or pulling up on emergency brake helps and/or stops noise. help!!! Its driving me crazy!
Car is a 94 Gt with a 5.0.

stock radio? got an amp in the trunk? sounds like bad wiring, look for help at http://www.crutchfield.com/S-wsYWapPXOm6/TechSupport/index.html?list=true&expression=engine+noise

that can be annoying. Does the feedback go up and down with the RPM's of the engine? There are filters you can buy to suppress the noise assuming the wiring is okay. Also if your spark plug wires are old and wore out you might try replacing them with some good suppression wires as plug wires can cause this problem.

Change your grounding point on the head unit. That will normally fix it.

Like Dan asked, do you have an amp?

that can be annoying. Does the feedback go up and down with the RPM's of the engine? There are filters you can buy to suppress the noise assuming the wiring is okay. Also if your spark plug wires are old and wore out you might try replacing them with some good suppression wires as plug wires can cause this problem.

Had the Mach 460 system in the car, thought the CD player was the
problem, has amp built into it. Replace radio, now has built in CD player and no amp but old CD player is still in dash filling hole.

Change your grounding point on the head unit. That will normally fix it.

I agree with SkylineUSA, humming is due to poor electrical grounding.
Don't spend money on any other solution until this is fixed.

i'm not all that up on stereos, but i know that if you dont' buy premium feed wire for a good system it'll cause that. also, if the wires feeding the amp are bad it'll the same thing.