well fook me.. it was the variator causing the noise!
I'd heard of the variator causing diesel noise... but not this weird on off power/load problem.
It must have been 'sticking' in a certain position or sommat.. maybe causing it to starve sommit of oil? not sure how that works/effects the oil flow? maybe the noise was from the variator? god only knows.
oh yeah and i thought i'd done sommat waaaaay wrong! the engine was ticking sommit scary loud when i'd started it up after re-fitting the bas back together (not the same as b4 noise)... put a wee bit of oil in... no differance.
'oh *****' i was thinking... i mean this was loud!!!!!!! turned off and on a few times still there. 'aww nooooooo' was the next thought.
For some unknown reason i disconnected the solenoid for the variator operation, dunno why, just did. started her up again... weyhay!!! noise gone.
erm hang on.. does that mean the control solenoid is fooked... nooooooooooooo.
turned her off, plugged it back on, started her up again... still no noise. noise has never come back. WTF was that about?!?!?!!
working ok now
thx for all suggestions and thank god it wasn't anything worse.