Clunk in my F250 when accelleating from a dead stop.

It's a ford f-250 7.3 diesel. 2WD.

I also have a leak in the front and have traced it back to this thing:



I think it's leaking out by the word "flow". Don't know if that's related to the clunk.

Here's what it looks like if you slide under the front bumper, a little starboard of center.



There is no fluid on the top side of the larger tube, just the right. And the right tube is just under the according looking thing that says "flow" on it.

I'm guessing someone will know what that is.