Antenna Noise

The antenna ground is bad.  It is probably grounded where it mounts to the body of the car.  I've seen this before...

we checked the ground though,that is where its grounded. gm went to good measures to insulate the ground. only option we can think of is maybe the antenna lines pinched and its grounding off onto the chassis?

Yea, that could be.  If the wire is pinched so that the inner conductor is touching cround you'd get a straight shot of engine noise into the receiver.

If the noise is on the Am band, then the problem is likely a poor ground on the antenna or the battery to the fender. Check the 10 gauge cable off the battery to the vehicles chassis. Clean it up and make sure it is tight and not corrodded. Measure the antenna's ground at the radio end of the antenna lead tip. You should get a reading of less than 1/2 ohm with the ignition off. Also measure the continuity through the center lead to the antenna tip. There shuld be no resistance. (less than 1/2 ohm). If the noise is on FM, then remove your distributor cap. Clean the contacts on the inside of the white debris. A inline capacitor can be purchased from GM (part # 3906145)and should be installed inline on the pink ignition wire going into the side of the distributor cap. (usually has a white plug on the end) If this fails to cure the problem, then you may have defective spark plug wires. If they haven't been replaced for 5 years or more, it may be time. Cheap plug wires aren't know to give good noise suppression. A quick test to reveal if your plug wires are really bad is to pull your car along side another. Run your engine with the hood open and listen to the other car's radoi. The other car shouldn't have the engine running. If there is noise on the other car then it's time to have a tune up on yours. Take the inline antenna noise filter off. They usually do more harm than good. sparky