I use to install CB radios for a living ... back in 1976 when we were happy to have 23 channels! I'm a ham now but will break out the old dusty Cobra and K40 out of storage one of these days.

For your SWR make sure you check both ends of your radio - you want the SWR to be a bit high on each end and "perfect" 1.1:1 in the middle at channel 20 - right next door to channel 19 where even after 30 years the truckers still live.

For your noise ... if it's a crackly static it might just be normal. Adjust your squelch up until it cuts out the back ground noise. If it's a pop-pop-pop that only is present when the truck is running it's a bad spark plug or wire. Normally resistor plugs and wires fix that. If the noise is a whirling that goes up and down with the RPM's it's alternator noise which is either a bad ground or a bad filter on the alternator - they sell filters for this noise at the CB stores.

Also check your radio to see if it has ANR - Automatic Noise Reduction and turn that guy on. It will hurt your very distant listening but make all other listening cleaner.

73's

KG6xxx