I have the antenna on the tailgate on a teraflex cb mount. and I cant remember where i grounded the cb. but come the spring time i think im going to re-do the whole wiring for it. after i was rear ended it was never right.
consider grounding the CB directly to your battery. On the TeraFlex CB mount did you scrape off some of the paint? Also, do you have an aftermarket stereo? I had the exact same problem you are describing and I have an aftermarket stereo. once I completed the steps above...no more interference!