My paint is starting to yellow on the rear bumper and along the doors.......will a clay bar treatment take this out? Its not rust I'm thinking but some sort of buildup......

Anyone out there get this on their itr white paint......I'm thinking its because there is no clear coat.

 

Clay will only get rid of surface contaminants and minor oxidization. If there is no clear coat, I'd say you are past the point of clay being able to fix this issue. You should post some pics. It would help to see what we are dealing with.