loud tapping/tacking noise when under normal load?

[Nev62]

Coming home to Sydney from the Watagans last night my 6.5GM diesel developed a very loud tapping/tacking noise when under normal load.

Prior to this I towed a broken arse FJ60 (nat84) from Gosford back to Sydney. Found going up steeper hills it would drop back to 40Kmh (was being rounded by trucks and 4 bangers towing large trailers). Taking the emtpy trailer back to Gosford, my 4b drove as per normal.

Thought I would see if I could find some friends camping in the Watagans so went for a drive and as mentioned on the way back going up a slight incline under normal load at 100Kmh (2000 RPMs) the loud tapping/tacking started (think of noisy tappets in an engine with low/no oil and turn the sound up 4 times). The oil level is ok, no heat problems, not reved over 2500 RPM and normally sitting between 1700 and 2000 RPM.

What has me buggered is that the noise is only there at normal loads (flat or slight incline/decline). Under light/no loads (down hill, coasting, idle or in neutral) or heavy loads (up hill, putting the boot in) the noise goes away ???

Anyone have any ideas before I start striping it down????

[6.5 rangie]

Is it still running ok? not an injecter

[ludacris]

Any chance of bad fuel.

LudaCris

[fullmetaljacket]

x2 on the injector.....they can get pretty damn noisey

[Nev62]

Is it still running ok? not an injecter

Still seems to be running ok. It is hard to diagnose what is making the sound as the noise is only there when under normal running load (prob need a dyno to reproduce normal loads).