Engine knock or transmission knock?

Hi everyone, I have been having issues with a clutch install that has been extremely stressful!I think my mechanic has gotten the throwout bearing issue fixed? Alli know is my 02 gt is knocking when in neutral without the clutch pushed in.If you push in the clutch while pressing gas in neutral you get no noise! It sounds like diesel sounding car when I push the gas down in neutral with the clutch up Strange ..The sound is coming from what appears to be just behind the drivers side front tire.It really sounds like a diesel best way to describe it!Does this sound like a rod knock? Has anyone ever had this before? My mechanic says there are play in the gears and they are rattling against each other or something like that,if this makes sense? If someone could please help me with any ideas that would be very appreciated! This is been driving me crazy!

Oh yeah,it never made this sound before the street pro clutch and mcleod flywheel was installed.There wasn't a peep coming from this car until they did the work,so would could have went wrong during installation? He did check the input shaft bearing said it was good.I feel something went wrong during installation but not quite sure.