Odd but loud noise on overrun.

Manual TD5 with Turbo Technics VGT and Allard intercooler, De-Cat'd and De-EGR'd.

I have what sounds like turbo whistle but it only occurs on overrun and only when facing down hill and it gets loud, starts like a normal turbo whistle and gets louder for a time the longer you are in overrun (it does reach a peak and gets no louder), the noise can be varied using the throttle with the clutch depressed so I know it is engine related. Once back on the flat it fades away again, it has proved impossible to reproduce on the driveway. It is like something is moving forward and rubbing on something that's spinning, but I can find nothing showing any signs of this.

The water pump is new, the serpentine belt is new, the tensioner is new, the oil cyclone 'filter' has been replaced with a genuine LR item. The A/C unit is secure with no play in the hub, same goes for the power steering and suspension pump, all oils have been replaced. The exhaust manifold has been refaced and all studs also replaced, it isn't blowing. When driving the car normally the sound does not exist, it only appears on overrun and only when going down hill.

I'm out of ideas - the only places this happens are those places where stopping to take a look would be utterly impossible, by the time you get to a place where you can stop - so has the noise - stopped.

I also have a very annoying 'buzzing' noise coming from the gearstick when the car is hot but I don't think these are related, this is definitely engine related.

I'd start by looking at the engine/gearbox mountings to make sure the engine is not moving forward on the overrun downhill.

Never really thought about that one, I shall put it on the list, I'm under the thing this weekend replacing the reversing switch and fitting a front push bar anyhow