I have a soft tapping in the ? engine that sounds like pock pock pock at each injection event and keeps time with the engine but can't be heard above 1800 rpm. This noise started after I put in a 5521 IP that I had the head off of before installation. I can only hear the noise in cab. under the engine and under the hood I hear nothing but diesel noise.

check to see if the fuel lines are touching the floor up by the bell housing i have heard a similar noise from this after doing a trans

I've been telling myself it's just the noise of the IP echoed of the vc or something.

QM

Check also to see if you have an injection line touching the heater hose. I had one do that once and it sure sounded like a main bearing going out.

Tim