From the sounds of it could be, but the problem with that it goes away. With an exhaust leak it usually never goes away and gets louder the faster you go, but road noise can hide it.
My turbocharged car sound like that, but it also had piston slap along with the leak at the manifold. My other turbocharged car that I fought with the exhaust manifold also would make sounds like this , but never quited down until tightening up the exhaust manifold.
So the manifold doesn't expand with heat, closing the gap?
I would bet on this. Are you burning any oil like smoke coming out of the exhaust. I couldn't see piston slap without oil getting past the rings.
I'm not burning any oil, and there isn't any smoke. But I do sometimes catch a whiff of a burnt oil smell. Overall though, i'm not losing any oil.
UPDATE:
I started it one morning at ~45 degrees. It made it's normal slapping noise, but this time there was a pinging noise, like metal hitting metal. It wasn't consistent though, it would ping only every few random seconds. Once it warmed up all of the noises stopped and the truck drove like normal. Since then I put a little bit of oil in before I start it in an effort to coat everything with oil. It hasn't made the pinging noise, but the other slappy noise is still there.
Also, the oil pressure is at 42 almost the whole time.
I'm living in the mountains now so I don't have internet or phone service, so my replies are few and far in between but I appreciate the replies.