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

Replace the universal joint. Refer to Universal Joint Replacement - External Snap Ring .

One or more of the universal joints have lost lubricant

Replace the universal joint. Refer to Universal Joint Replacement - External Snap Ring .

The yoke retainer strap bolts are loose

Tighten the yoke retainer strap bolts to specifications. Refer to Fastener Tightening Specifications .