Proform 850 dialing it in closer

tjpatte said
Check to make sure you don’t have a plug wire in the cap arcing to the windshield wiper motor bolt. I had bad radio noise for about a year and tried filters, wiring directly to the battery and everything else. Since I didn’t listen to the radio much I just left it turned off. One day while setting timing I turned the garage lights off to see the marks better. Happened to look towards the windshield and saw the arc. Repositioned the distributor and replaced the boot and all is well. The arcing didn’t effect the running of the car and if I hadn’t turned off the lights I would have never known.

It can be tight there.
I don't know how much it helped but an old trick I used was placing a short section of fuel hole over the sprak plug wire nearest the wiper motor. Maybe four inches long and cut lengthtwise so it could be be slipped over the wire.

I do not know enough about the relationship between electrical noise and electromagnetic interference to suggest quick ways to tell them apart.
I assume the first would show up on an oscilliscope.
Both @KitCarlson and @halifaxhops may have some perspectives on this.