Audio Systems: Interferance, static noise, ford truck

Question
My radio in my '94 ford truck has a lot of noise, static etc. on certain AM sta's. When I shut off engine it clears up.

Answer
new noise supression type spark wires, go through engine compartment and tighten all grounds you can find, if you have a whine that changes frequency with engine speed, install supression capacitors on output and field of alternator or replace it.(never use advance auto electronic parts) if it is a rushing static noise, better plugs and wires are needed. i also have a 94 ford explorer.....