I can almost guarantee you that the pinion/spur mesh is too tight. You want to be able to "wiggle" the spur gear slightly against the pinion. Check out the owners manual as it explains this with pictures.
Also, you may have damaged the spur and possibly even the pinion. You may want to replace them. Yes, 64 pitch gears will be quieter, but the car should still be pretty quiet even running 48 pitch.