Driveline "clunk"

[P STK DZL]

Hey guys,

I have a 1997 F-350 with a 5 speed and recently I have felt a clunk in the driveline when the clutch is fully let out. It is easy to feel in 1st and 2nd gear and slightly in 3rd and 4th. There is no whining or grinding coming from the transmission or rear end. I thought maybe I needed u joints on the rear driveshaft but there is not a lot of play in them. Could something be loose? My friend noticed when I came to a stop in his driveway the front drive shaft looked to push the front diff down like it was still wanting to move forward. Let me know you what you think the problem could be.

Thanks for your help,
Mike

[oasis04]

Motor mount? Should be no play in u-joints. Why is front shaft moving at all? Leaf spring shackle bushings?
I don't know I am just spitballin ideas?