A clunk when accelerating, lifting off the accelerator, or engaging a gear may come from excessive movement somewhere in the drivetrain. Possible sources include differential wear, driveshaft joints, axle splines, or engine and transmission mounts.
Some driveline clearance is normal, and certain differential designs have characteristic operating sounds. A new or worsening clunk should still be investigated, especially if it occurs with vibration or harsh engagement.
Certified Transmission in Council Bluffs, IA can inspect the related components to help identify where the movement or noise originates.