Agreed with PapaKB check your antenna. If your antenna is way out with its swr the noise will be louder than the signal. Also, are you using an inverter, 24 to 12 volts, or hooking up to the first battery? I am not sure how noisy the electronic inverters are if you are using one.
The other possibility is that the alternator is partlly snafu and the noise if from stray a/c due to leaky diodes. If you think about it, the alternator is the only potential source of noise in the electrical system. You could disconnect the field wire and start the truck and see if the noise is gone. If it is, then you can consider having the alternator checked out or replacing it.
Hope this helps
RL