Def sounds like an exhaust leak to me. Check your manifold isn't cracked as well. Mine had a crack right inbetween some runners and made a similar sound. Using a mechanics stethoscope will help you narrow down where the sound is coming from.

 

You can do the leaf blower/shop vac test. Tape the leaf blower outlet to the exhaust pipe and turn on, spray windex on the exhaust manifold and pipes and look for bubbles. Sounds like an externally blown hg to me.

 

A length of hose - one end to your ear and the other end move around down there to pinpoint the sound.

 

ok, so I started her up last night. I did find some puffing on the right side of the motor if you were standing in front of the truck looking at it. I have to clean up the area bc it looks to be leaking a bit from many places. I will clean it up with some brake clean. I also found my coolant reservoir was basically showing empty, so I added the proper coolant did look as if someone put green in, so not sure if that will cause any damage. Digging into it this weekend. Praying for an exhaust leak as I am dreading doing the head gasket as I have never done one before.

 

It is possible that a spark plug is cross threaded or not fully torqued?

 

I haven’t attempted to remove them or torque them. I’m going to attempt a smoke test tomorrow.