Strange Rumble Grind Type Noise

neilly said:

Why did you have diff lock on? was it slippery? not read a max speed for diff lock to be used, just seemed a little high for using it when it would normally be used when the conditions are a bit slippery.

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No it wasnt slippery, It was down to finding out this noise, I also noticed when pulling off from the lights there is a delay in lock from the transfer box, like a thud where the gears are engaging. So when I engaged Diff lock this was basically eliminated, making me think my Transferbox is on its way out.

neilly said:

which diff was welded? diff lock only works on the ctr diff on a disco.

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I agree, it does only lock the centre transfer box diff... But I use to drive a BMW 525i with a welded rear diff, full active rear end. This has nothing to do with my problem though. i just thought i would say ive locked diffs before.

Someone mentioned that it could be a few gears rattling...

Any ideas? Don't want to die on the motorway...