It's quite likely external of your vehicle then.
Find a dirt road somewhere that is well away from other houses, businesses, power lines, etc., shut the engine off (shut everything off except your CB unit) and then see if you still have static. If you do, then something is likely amiss with your radio (or it just doesn't like that antenna or something).
If the static isn't present, then you were just in a noisy area.
Static interference around electrical/electronic equipment/populated areas is often a way of life nowadays on HF/low-VHF bands, which includes CB (I have someone down the street I suspect might be running a million watts of marijuana grow lights that spews out S-9+20dB of raucous wideband static from 10-50MHz when I drive past his house). Fortunately crap like this isn't an issue when you're away from town.