Gymbag said:
Ok just a little more info.........I usually just run with the battery pack but do have a cigarette lighter adpater and using only the rubber duck antenna, it is more noticable in the 150.000-168.000 range.
If I had to guess, probably your trucks computer. More common sources of interference are high voltage ignition (tic, tic, tic), and alternator noise (variable whining), as others have mentioned. But if it's primarily limited in that range, I'd say it's the computer. You might try calling the service department at a dealership. If this was a common problem, it's probably been documented by amateur radio operators, and may be in their records.
Running off the radio's batteries, and using an external roof mounted antenna would probably help a lot.