Technical Tapping noise

[Plumbbob]

Hello I am new here and require help.
Whilst traveling at speed the engine has developed a tapping noise. Sounds like a noisy diesel.
Vehicle is a 1.9D Cargo.
Power does not seem reduced, but I took it easy once I noticed the noise! Seems to come from the rear of the engine, maybe the injector pump?

Difficult to tell and I cannot find any good service manuals, can anyone recommend one?

Please advise

 

[xs1100e]

My 1.9D did the same, turned out to be the Alternator belt tensioner easy to replace if you have the right kit.