c15 bull gear

does the c15 have a bull gear like the detroit i have a rapping noise in the front gear case ran fine when i parked it now it has this rap i used a hose to locate the noise seams to be left of the idler gear i took the idler gear out and see nothing wrong truck has over million miles on it idler and cam gear are fine

 

oil is new couple thousand mile on it still clear not the compressor i took that off started it with out compressor was a mess but i tryed it if i turn the motor over with the solinoid i can here the noise too on the other side of the idler gear not the compressor side its a fast rapping or knocking to fast for a rist pin or bearing

 

not sure why the noise was in the front cover but i ran the over head and noise went right away injectors where way tight so i set them on the lower step on the cat tool maybe was back lash it the gears not sure sounds good at the moment