Well I fitted the expansion hose from this kit (P/N 03G131055AR) :
http://www.ebay.co.uk/itm/VW-PASSAT-EGR-HOSES-03G131055AR-NEW-GENUINE-VW-PART-/370349265842
Only the expansion hose/chamber is needed on the Leon 2.0 TDI.
I presume the kit is generic and the other hoses fit elsewhere on other VAG (that's what some google images would seem to suggest)
By googling the separate P/N that is on the expansion hose (P/N 03G129808C) I managed to find an image showing it's location.
The reason I could not find where it fitted, after searching under the bonnet, is that it is a replacement for a standard hose. So in standard form you will not find a hose looking like this
Image found on google :
It just inserts the expansion chamber, and therefore causing a slight difference in pressure on the internals of the BCS (Boost Control Solenoid) and therefore stops it rattling.
Despite this kit being described as an EGR Hose kit, it has nothing to do with the EGR.
It replaces/connects to the vent pipe of the boost control solenoid (mounted on the bulkhead) which vents surplus air back into the air intake. This vents air away from the turbo actuator under ECU control and therefore allowing the ECU to control boost pressure.
After fitting the noise I had from around 1,200rpm to 1,500rpm is very much reduced.
The sound it still there but only because I am really listening for it, and if I hadn't heard it before I would not notice it.
Quite a good modification for the money, as it has turned what sounded like a grumbling turbo into a near un-noticeable noise.
I presume that at 1,500rpm when boost is just starting to be generated there is a slight pressure miss-match between the induction through the airfilter and the venting of the BCS. Therefore causing the internals of the BCS to rattle. Inserting the expansion chamber corrects this miss-match.
The same modification could be made even cheaper by blanking off where this pipe would normally enter the air intake (just above the air-filter) and venting the BCS to atmosphere.
This should be perfectly fine to run as I know of other cars with a similar arrangement that vent to atmosphere if an induction kit is fitted or if the nipple attachment to the air-intake gets snapped/broken off.
My Fitting