Gazelle, clunk when pulling away

[styleruk]

HI

I am very slowly restoring my old 65 Gazelle (Mrs. Ings), She has done a ton of miles and whilst I have now finished all the welding last year, I stripped the engine and rebuilt it but it was worn in places so will need coming out this winter. So I put her on the road and have been using her for the odd trick and a couple of long trips here and there (pleasure only). Lately she has developed a clunk noise when I pull away, immediately I thought rear diff because when I drained the oil last year a few very small fragments of metal were in the oil and I thought, well the diff will need doing soon, so I'm thinking that.
This morning I drained the oil again, it was clean after 1 year of use with no metal fragments. I still think it's related to that because it seems so loose, but I'm doubting it a bit as it is a big job to do that.
Checked the wheels, OK.
UJs...OK
Engine mounts...OK
Engine to gearbox mounts...OK
Bottom of struts and suspension...all seem tight
Brakes, as in rear drums...seem ok, they don't rotate or seem loose. Refitted them last year so they all look brand new.

Running out of ideas now, anyone have any ideas what to check next before I consider a diff strip!

Thanks
Simon

[jeans_old_man]

Spare wheel loose? Exhaust touching bodywork? or could it be that marble in the ash tray?

[mikeyr]

driveshaft u-joints.