Engine Clatter/Thrashing when touching accelerator???

Hi each and all, completed the replacement engine on my 1.5 DCI Van, a few little problems have manifested themself, when the car is started from stone cold there is no Clatter/Thrashing noise for a few minutes, then it will start clattering/thrashing that will fade out and dissapear at about 2500 RPM, it is doing my head in as the engine drives fine, it has only done 63000 miles, it has had a new timing belt kit fitted, oil and filter change, fuel filter change, air filter, clutch kit, slave cylinder, when the engine warms up to temp the noise does fade out a bit, you can feather the rattle clatter by just touching the accelerator peddle, off and on = clatter or no clatter

any ideas? anyone had a similar problem?



Hoping for some ideas on this.



Best wishes Darren