I'd check your gound for your cb and your radio. do you get feedback when just the radio is on or all the time. Your cb emits interference which your radio might be picking up if thier right next to each other. An in line noise eliminator might also cure the problem.
Unfortunatly there is nothing you can do. The feed back you getting is radiated and it can feed through the radio and also the speaker wires. most of the new radios with RDS have a problem with this on the hiway with 18 wheelers and cell phones. Powerfull CB's can over take just about any radio out there especialy cheap radio's.