Answer: Half the fun of going mobile is getting the noise
down to a low roar. You have already determined one thing when
you removed the antenna and the noise went away. This indicates
the RFI is radiated and not coming through the wiring. Make
sure that your hood is grounded. Sometimes the factory system
isn't enough for communication type radio. You may have to run
a braid (at least 1 in wide) from the hood (near the hinge)
to the chassis. Keep it short. That is a good first try because
some sort of shielding (more complicated) would probably be
*ED. NOTE: Under the advisement of our Technical Guru, I visited
a website that had to do with the noise that is described above.
The long and short of it said to ground not only the hood, but
ground everything. So, I did like the article said: I
grounded the cab, which "floats" on rubber insulators,
to the bed, which is bolted directly to the frame, via a braided
flat cable. Ditto on the hood, ditto on the exhaust system.
That also rides on rubber insulators, and acts as
a big antenna! After all that, no luck...still the same noise.
I got to looking at the way I have the antennas mounted...on
a bar across the bed. It's bolted to the top of the bed, but.....
what the heck, I'll re-ground that too. VOILA! Noise
gone! Just for grins, I un-did one of the previous grounds,
and the noise came back. The moral of the story: Ground, ground,