One or more of the universal joints are worn or damaged.

Replace the universal joint. Refer to Universal Joint and Slip Yoke Replacement .

One or more of the universal joints have lost lubricant

Replace the universal joint. Refer to Universal Joint and Slip Yoke Replacement .

The propeller shaft retaining strap bolts are loose

Tighten the yoke retainer strap bolts to specifications. Refer to One-Piece Propeller Shaft Replacement or Two-Piece Propeller Shaft Replacement .