My 1994 F-150 has AM static with the Key in the "on" position but no static with the key in the "acc" position without the engine running. With the engine running you can hear noise from the ignition system. Is the PCM causing this? What can be done to eliminate the noise?

 

An RF filter from Radio Shack or an autoparts store will probably fix it for less than $10. You could also consider a new set of plug wires if yours haven't been changed in a while.

 

Could be ststic from the fuel pump KOEO. the pump should only run and cause interference for a few seconds. There are also plenty of other electrical actuators running KOEO. IAC, TAB and TAD, ETC. I am sure it is not anything too serious

 

sometimes this is just a bad radio ground and you are picking up radio waves/interference from engine electric parts.

Run a new radio ground to the frame.