Voltage Drops During Idle

[wildbill23c]

Good work

yes, lower coil voltage = lower spark voltage

radio noise is fairly easy to identify
Does noise change with engine RPM?
If yes then alternator, coil or spark plug wires are the issue.

Any electric motor like blower fan or fuel pump can cause radio noise

Antenna's base must be properly grounded to body, and so to the Radio chassis, or the antenna is just doing what is suppose to do, pick up RF waves, but thru the BODY of the truck.
So this is the very first thing to check.

Cold engine
Loosen fan belt and take it off alternator
Start engine, see if radio noise is gone, if not then alternator is not the source.
If noise is gone then you need to add suppressor to alternator

For the rest read here: https://www.howacarworks.com/accessories/identifying-and-suppressing-radio-interference

Well a quick check ruled out the alternator causing the noise, I started the vehicle without the belt attached to the alternator, still the same noise. Don't feel like tearing the dash apart to get to the back of the radio right now. Noise doesn't change with engine speed, and its only on FM stations. Its pretty frequent, but it seems like after I drive around and the vehicle warms up completely like after a 15 mile drive for example then I can listen to certain stations on FM without the squealing...its extremely weird. If I try and transmit from my CB radio the receiving party gets a bunch of noise as well, now if I'm parked with the engine shut off the radio works fine as does the CB. So there's something going on somewhere for sure. I suspect a bad or loose ground somewhere which is not gonna be an easy thing to track down.