TD6 Diesel Noisy

Hi,
Since returning from holiday towing the caravan, the engine sounds much noisier with a definite cammy tap to it. It is worse when cold but very evident on the move as if the tappets needed adjusting or a hydraulic tappet had failed. Does anyone out there know if there are hydraulic tappets in this motor. I seem to remember reading modern diesels give several fuel squirts to smooth out the detonation cycle, could it be injectors?
I've only done 2500 miles since the last oil change but i'll change it over the weekend to see if that helps, any reccommendations on the benefits of engine flushing oil would be most welcome.
Other than the noise the motor runs fine and starts hot or cold with no problems.
Thanks in advance.

Long run, engine oil consumed, have you checked the level?

The motor does indeed have hydraulic tappets.

Did you change anything with the last oil change, a different spec oil perhaps? Is there something loose on the engine that is transmitting the noise, a broken bracket perhaps? Sticking your head under the bonnet with engine running and have a look/feel around. (Be careful though, that doesn't sound very safe!)