Clunk in Idle "Crawl"

[hammerg26]

Today in carpool, I was creeping along in idle and notice a clunk (felt like once per revolution of something)... I felt it going straight and while making a slow turn. I do not notice anything with any sort of power, but perhaps it is happening so rapidly (many RPMs) that I don't notice it. The clunk FEELS like it is coming from the front of the truck. All fluids are fresh (and have been since I got the truck at 72K miles 3 years ago - presently at 166K).
Thoughts? Really not sure where to start troubleshooting.
Thanks.

 

[Bedrck47]

Check the u-joints on the drive shafts Jack up the front end and turn each wheel by hand and listen