I get to feel an engine vibration / harshness possibly at around 2500 rpm which occurs when the transfer case mount bracket is filled with hardened mud. I dig out the hard dirt with a big screw-driver.

I have run it with the longer drive belt off and made little to no difference.
I have ordered a fan pulley. So will run it with that belt off too. Will check crank pulley at same time.

The tapping only appears after engine has warmed up also, can be heard loudly through the front grill. Use a mechanic scope the sound definitely originates from the HPFP, sounds like a bag of nails through that. The noise is not engine speed reliant.

No significant vibration, slight felt when slowing done and engine drops below 1000 revs briefly

By design they are obviously quite noisy hence the soundproofing. The tdv8 is a particularly quiet engine compared to most Diesels.
The part number changed a few times, not sure if part was slightly redesigned.

The rubber damper on the crancshaft pully failed on my car.With car idle use a strong torch to check the pully for wobble.There was no vibration of engine. 2012 TDV8 Vogue SE 4.4

Ticking noise gone.

I have run two tanks of fuel with injector cleaner additive and the noise has reduced to barely noticeable.

What magic brew did you use?

Carlube Diesel Fuel Injector Cleaner

I bought it from Sainsbury’s , £4.99.

Was recommended by MB master mechanic, he said they use it all the time on Mercs that fail MOT’s. He advises every 4th tank full on an ongoing process.

https://video.fosl4-1.fna.fbcdn.net/v/t42....F&dl=1
the mecanic says see for a new pump....