Thanks etcha. I took the wheel off again and turned it by hand, definitely a catch somewhere. Next I tried etcha's idea with the screw driver. Sure nuff, there was a variation in sound but not on the horizontal cam. I put oil everywhere, including the bevel gears( good to know what they are called). I've got to get some gear grease but I suspect its the same thing my DH used to service big rigs. Anyway, the knock is gone. Youse guys are the greatest.