The best that I can find/think is in the area of the transmission and engine mating area. At first I was thinking converter or pump but someone suggested flex plate, how ever as stated when I pulled the cover I didn’t see a crack but I could not see where the plate mates to the engine.

 

I don't think it's a cracked flexplate, that would be a completely different kind of noise. Maybe have a look at the engine/trans mounts.... the rubber may have broken down, and you are getting metal to metal contact. That'll make some rude noises.

 

I’ll try and take a quick peak tomorrow after work and report back. I appreciate it.

 

looked at it yesterday and didn’t see anything. All mounts looked good 🤦🏻‍♂️.

 

Need to work 'em a bit. Stick a pry bar in there, and see if the mounts, are actually still mounts.

 

Finally had a chance to do this. They’re solid. Didn’t move against my big fat a** and 36 inch pry bar.

 

Check everything that has rubber isolated mounts..... (exhaust?) That's a fairly heavy knock......

 

I’ll do more investigating Friday when I get to the shop and fix the plenum leak. Listening to it today with the hood open I’m going to pull the belt and check the alternator and idler pulley.

 

Obviously haven’t had enough time to run the truck since doing the plenum gasket and all but do have a question, I didn’t replace the timing chain or gear while doing the gasket the other day as my truck only had 111,500 miles on it, but the chain had maybe 1/2 inch of play. That said. Could that noise be that? I’d think it would have broke by now if that’s what it was.

 

Probably not. More likely a small exhaust leak, or something similar.