Can you tell if the tap noise is coming from the front or back of the motor? Injector pump or injector pump timing? it sounds mechanical maybe even a dropped valve or somthing. Hard to tell on a recording. I had a similar noise on my 3 ltr but not as bad. Turned out to be the end of a glow plug had dropped into the cylinder and bounced around on the top of the piston. It wasn't that noisy though.