I have a 2000 f350 with 7.3. I have the same problem and traced it to the computer. I used a small battery radio and moved it around the truck till I found the worst interference. It was coming from the right (passenger) side of the dash behind the glove compartment. It is worse at low frequencies such as 540 AM and gets less toward the higher frequencies. Smart a$$ remarks as switch to fm do not help as most of the programming is aimed at 12 year old kids. I have not found a cure except improving the ground to nthe radio and antenna. Maybe a ground to the computer would help.