Spark Plug Noise through radio

I'm one of the few out there who still like listening to AM radio, problem being, I'm getting "Spark Plug Noise" when the engine is on. I've had an aftermarket Alpine radio (that AM worked fine on with another vehicle) installed in my 91 GMC Sierra. FM Radio works great, but I'm getting interferrence with all AM stations. THe installer can't seem to find where the problem is, even after trying a new antennea, etc. I've also replaced the braided engine ground straps. Anyone have any other ideas of what the solution may be? I'm at a loss...

I don't know much about it since I've never encountered the problem myself, but I do know that there are filters that can be put onto the ignition system somehow. Try asking you local auto parts store about it.

Its Usually A Bad Ground Back Feeding On You Ignition Ie Radio
Check Your Motor Ground Strap And Your Ground On Your New Head Unit (cd Player) Also Could Be A Chassis Ground

I had the same problem, i listen to am for the trafic reports, my problem was resolved by acident when i replaced my stack coil with an after market unit