Excuse my ignorance Taz Turbo. But wouldn't we get stuff either in the diff oil or stuck to the magnetic drain plug on the diff if it was this then?

Pully bolt would perhaps bang then clatter as it passed under the car but would not produce noise for the rest of the trip.

Prop shaft UJ gets my vote. The vibration was it out of balance as the needle bearing broke up. The scuff marks are it running out of true.
I know you have checked but I would check again particularly as you say there is some play. A good joint will have no play you can discern by hand.
Try both twisting the joint and push/pull in each plane of the joint.

Steve

Trouble is if the pinion front bearing as failed on the GKN then the shed material from the bearing will stay in the nose of the diff (you cant drain that area) so when you drain the diff you will be lucky to remove any swarf if any basically the drain plug is not in the lowest part of the diff on the GKN but of course this wont be Barreti's problem we hope

An update chaps, though sadly still no resolution.

I couldn't find anything wrong after inspecting/pulling/pushing/turning everything I could see or get my hands to under the car.

So with the back wheels off and the car on axle stands I started it up. In both neutral and throughout the gear range. I drove it through every gear, to approx 3000rpm and an indicated 40mph in 5th gear. And did this test a couple of times with the engine off between the 'runs'

There was nothing. Not a squeak - other than from my bum! Being sat 3ft in the air in my garage with an indicated 40mph is a bit cheek clenching!
In fact it sounded better than ever because I've probably refitted the exhaust better.

I've now road tested it and the noise was evident before we even got off the drive.

So here is what we found

The noise is only there under load but it is obvious as soon as I start to move.
It disappears when freewheeling both with the clutch depressed and the car in gear or with the car in neutral.
The noise is NOT evident when the car is travelling in reverse at up to approx 10-15mph
The noise DOES NOT change if the car is driven around left or right corners.
The noise has a definite rhythmn.
It isn't a metallic rattle as I said earlier, it is a thump thump.
It sounds a bit like a chug chug as if the exhaust is blowing. BUT ITS NOT THE EXHAUST.

It sounds like an old steam road roller driving down the road!

I think it might be the rear propshaft UJ
Does this sound like a fair guess?

Have you checked for any tyre deformation? They can sound like a failing CV joint.

I am with simon on this one. Its easier to check cv's than diff so start with cv's. I think you are going to have to take each drive shaft off and inspect them properly. Its going to be cv or diff , heres hoping its a cv.

Agree with the last 2 posts Ian, I think you may have to have a strip down may of been covered already but are you sure the prop is not banging on the exhaust through there being excess movement in a prop UJ ? I am still with the failing CV joint though if they are swapped round to run in the opposite direction the problem normally never reoccurs

Wheel bearing on the way out but only showing symptoms under load?

As the exhaust etc is off - you might as well check the front pinion nut is tight .. as this is know to loosen with a collapseable crush bearing.

Use a pen or chalk to mark the prop / axle then undo the 4 prop bolts.

Move the prop to one side, and check the large pinion bolt is tight. Someone might need to press the foot brake while doing this ..

Remember to align the prop with the chalk marks afterwards.

It's only 4 bolts so does not take long and eliminates a common problem on the Griff.

p.s. I think what your mate in the Chim actually said was - is your handbrake on .. because you could not keep up with the superior car

Snapping teeth like that is often caused by the pinion nut being loose.