[baD]

cheers for the input

More info/detail
After putting a new spur on the FS2 it sounds perfect, sweet as a nut. Then after a good run or two it sounds like a first generation pred ! I do wonder if the chassis material is such that it exaggerates/amplifies the noise rather than absorbs it. Seems to be a totally different material from all other cars I've had.

The spur is nowhere near any tie rod or anything else, just the pinion.
The pinion(s) is/are in good nick
The wear is only ever the tops of the teeth - it doesn't take them down to bald, it doesn't wear it in patches, but takes the tops off all teeth.
I'll check for distorted plate - it never occurred to me something this thick could bend/distort.
Diffs are smooth - on the loose side if anything.
Never stripped any teeth from either diffs - they are both aok

the investigation continues .........

PS - gonna ensure the mesh is changed from a nats knacker to a baby nats knacker from now on, or at least till I can find what's causing this.