So this project truck I've been working on (6.9L / ZF) makes a noise that I'm not sure is normal. My intuition says it might be the clutch.

It sounds like a kind of mechanical, metallic snort at low speeds, when I either let the revs get too low, start in too high of a gear, or upshift too early.

If on the other hand I increase the revs, and then let the clutch out it does not make the sound, so maybe these engine just sound like that when you lug them at low speeds. I'm not sure.

 

Yup, sounds like mine. I think it's just a little too slow for it. I try to keep it up at 700+rpm when starting, and it doesn't happen.
Trying to start out at idle, mine sounds like yours.