I guess that slot cars have oval front axle holes to compensate for a warped chassis. The easy solution to the noise problem is just to turn up the music. On a serious note, if you run without magnets the front end of the car is nearly as important as the back. You need to keep the front tires firmly on the track and anything that wants to shake around will induce vibrations in the chassis that will degrade handling to some extent. With my NSR Mosler I fixed the sloppy front axle by threading some fine wire between the axle and the axle carrier, looping that over the top and twisting the ends together. A smidge of glue keeps the wire in place.