I have a 94 7.3 idi factory turbo has 378k on it and I’ve been noticing a knocking wile the rpm’s drop but I can only hear it in the cab, if I’m right over the motor with someone Reving it it sounds completely normal any help would be appreciated

 

check the flex plate. sounds like it my be cracked.
when failing they make noise on deceleration, but not on acceleration.

 

I don't hear anything, but a cracked flexplate sounds like you threw a rod bearing. It cracks like this:






That happened on my F450, many years back now. Had me worried, until I remembered it could just be the flexplate. Once I got to the job, I got under and took a look (after stopping to check the oil) and I saw that. Needless to say, I was very relieved. Tom's right. Sound goes right away under load, but you'd swear she was coming apart on deceleration.

With my M code (factory non turbo engine) I replaced it with ATP Automotive Z-344 (not externally balanced for a factory turbo engine!) Back along, the aftermarket didn't use to offer a factory turbo idi flexplate. Folks were left with sourcing used. I hope things have changed.