this could be a lot of things...
*check the front wheels free spinning ability*
*Check the magnet's alignment*
*Remove any metallic particles picked up by magnet*
*Check to make sure your steering return spring is not all bent up*
*Try tire rotations and such*
*try it without the body on (possible rubbing?)
that's all I can think of right now.
Visit
http://www.questformadness.com
Oh yeah and DO THE SPRING SAFER MOD FIRST THING IF YOU PLAN ON OPENING UP THE FRONT END!
I also suggest that you open the front end up somewhere that if you do have a tiny spring go flying it will be easy to find! like a bathroom with tiles. (toilet lid down, I can imagine bad things there!)
Good Luck
-Sketch