It's probably either driveline vibration where the angle is a little steeper or something may be a little loose or springs soft and let your axle wrap up when u get on it and binding the u joint up. Usually if its driveline vibration though when u let off and it cruises w no load it will make a grinding sound
I assume angle would be a little steeper since the axle was move forward 7.5 inches from original spot. Pinion angle was corrected and reduce the vibration by 75%.. Im so sure the CV ball joint area has something to do with it..
