RF Feedback in a Mobile

[Ed in Tx]

Since you didn't mention the make of your car, you might check here for your specific auto manufacturer's guidelines or information on installing 2-way radio equipment.

http://www.arrl.org/auto-manufacturer-s-policies


But as bob91343 said there's no panacea. Every installation is different, and what happens at one frequency may not happen at any other. I'd recommend studying the recommended installation methods, try it and go from there.