Strange Clunk

[BigMikeO]

Truck specs are in my signature below.
When I Start up the truck and put it in drive. I move about 100' and then i hear this clunk. I can't figure out where it is coming from and I don't feel anything when the noise happens.
It only happens in drive, because when I reverse it out of the garage down a 125' driveway there is no clunk, but once I put it in drive about 100' later there is the clunk.
I know this is not discriptive at all but hopefully someone here has had this happen before.

[Johnny B.]

I haven't had the problem, but try checking the following if you haven't already:

1.Motor mounts
2.Trans mount on the tail- mine was broke "rubber", but only caused vibration.
3.U joints
4.Ball joints

Where is the clunk coming from?

[damork]

If you have an automatic, check the speed sensor in the tail section of the transfer case. As your miles add up, the sensor can build up with junk on the tip and cause a driveline clunk when you take off from a dead stop (transmission signals seem to become garbled and they don't shift right, especially at low speeds). It's a 5 minute job.