1999 Ram 5.9l 4x4.
I started it and a second or so after I heard a clunk that sounds like the rear end clunk when you put it in reverse but it sounded like it was more toward the middle of the truck instead of all the way back at the rear end.
The truck wasn't moving and was still in park on flat ground. So, any ideas?

Also, my dad put the truck in 4x4 low the other day and said he heard a clunking/clanking from the front end when he hit the gas so he put it back in 2hi and it was fine after that. He said that it didn't grind beyond the initial grind during the shift.
I need to pull the front differential cover and the cad housing to check into that but ideas for that would be good too. I'm thinking maybe the shift collar hadn't slipped onto the splines all the way due to low vacuum but I'm not sure yet. Now that I think of it, I bought a vacuum tester the other day so I'll know a little more when I look into it.

 

have a look at the exhaust, that's about the only thing I can think of that would clunk after starting..... especially when you are still in park.

 

That's something I didn't think about.
I'll check that transmission mount too. Since the engine is bolted to the transmission then if that thing were squishy then it could allow the engine to rock more than it should and that could make the exhaust smack something. But It was only one clunk, that's what has me scratching my head.