driveshaft clunk

[6.2]

the past few days i have been hearing/feeling a clunk when going into reverse. or drive, or from reverse into drive, etc. so I took my gopro and stuck it underneath to see what happens. has only been happening the past few days. maybe for a week now. truck is an 06 FX4 level II. has 170,000 kms (105K miles) on it, and ive had it since 113,000 kms (70K miles). this is the first issue i've had so far.

heres the video documenting whats happening. Any ideas as to what is causing this?
oh, and a quick little exhaust clip included haha.

http://www.youtube.com/watch?v=9tv2VKEwFgI

 

[PanamaExpat]

Look for a bad U-joint

 

[doorgunner]

1. What rpm does the engine idle at?
2. How much rotation (slack) does the driveshft have with the engine off & transmission in Park/1st gear?

My '36 A/T does the Ranger CLUNK above 700 rpm....I'm wondering if I can shim the ring/pinion a little tighter to quieten the engagement since u-joints on the 1piece driveshaft are new?

 

[6.2]

Crawled under neath today. It's a bad u joint.

 

[PanamaExpat]

Aren't you glad it was that simple?

 

[6.2]

Yep. Will get a new one, and replace it.

Thought it was that a while ago when I had a slight vibration, but there was zero play in It at the time.

 

[6.2]

Ok. Now which one do I need.

There's about a million if the same part but different part numbers.....

Rear driveshaft. Both joints (may as well do both while I got it off)

There's like ten of the exact same thing.