i have a cb and a amp in the rear when i use the cb i can hear it in the rear speakers. y?

 

Its very easy for speakers to pick up a CB signal. Ive seen speakers on a home computer pickup up the AM signal of truckers on the nearby interstate.

Try grounding everything at ONE place, and keep your speaker/signal wires as far away from your CB wires as you can. Adding some shielding to the wires can help too.