at one particular point in the rev range I hear a noise coming from the what would appear to be the front turbo side of the engine, this happens at exactly 2500rpm on acceleration and again as the revs drop thru. 2500rpm on over run, this is most audible when the car is fully warmed up, the noise can best be described as that heard when driving over gravel.
I asked one of the mechanics at adealer close by to have a listen but, sods law, it did not happen then as the car was too cold.
any thoughts please?

Kenny, maybe somthing different, but I had a strange rattle when accelerating through that part of the rev range your talking about. Eventual cause?....Stone trapped in the heat-shield. Worth a look, could have half your drive-way stuffed up there!

KENNY we had a vehicle with a strange noise at a low rev range it turned out to be a loose hose clip on the interccoler hose when the turbo started to build up boost it was blowing out past the hose and clip.
just a long shot but easily checked.
peter.

Kenny

This sounds like a cracked heat shield. Check the shield which cover the manifold at the front of the engine bay, drivers side.

These were prone to cracking, especially at this time of year, as water could splash onto them giving thermal shock.

Later cars have a plastic tray under the engine bay which prevents this damage.

There is an item on http://www.sidc.co.uk/faq about this.

Pete