2000 mack rd 688 popping noise in drive line.

Check all Universal joints and play on every part of the drive shaft and yokes. Make sure the differential locks are not engaged or trying to engage.

Had a delivery truck with a tandem axles with a maybe the same problem.
One of the axle's differential would lockup one side turning to the right and bunny hop around a tight turn or even sometimes backing up.
The switch on the dash was off but it would randomly do this once and a while.

It could be the same problem, or maybe not.

 

If it's got Mack axles, the power divider (even if you have an air-lock switch) is automatic. If your tires are mismatched on the axles (i.e. you bought 4 new tires and put them across the rear axle and left the 4 worn tires on the front axle) the speed differential between the front & rear axles can be sufficient to cause popping. Always make sure your tires are matched up as close as possible, so that the input shaft on the front axle is turning just as fast as the input shaft on the rear axle. Same goes for side-to-side tire wear...try to balance left side and right side tires, because Mack rears aren't "open" like Eaton or Meritor rears, and taller tires on one side will burn up the differential.