So just in case anyone's intersted, the conclusion of this https://www.lfgss.com/comments/16871982/ is essentially that my hand was forced a bit as I was looking more closely at the rear wheel and quite a few of the nipples were visibly corroded and in fact a few were cracked - one flaked to bits at the slightest touch, so I've had the wheel rebuilt with brass nipples and CX-Ray spokes and bearings all replaced as well. All feels perfect and runs quietly and smoothly, finally! So, sounds like the issue was any of the spokes, corroding nipples or worn bearings - can't tell which but glad to have sorted it!
On other news, was putting it all back together and noticed the surface finish of the not that old Ultegra Di2 rear mech is flaking off and looks corroded underneath, so next thing to sort isn't far behind, depressingly enough...
So just in case anyone's intersted, the conclusion of this https://www.lfgss.com/comments/16871982/ is essentially that my hand was forced a bit as I was looking more closely at the rear wheel and quite a few of the nipples were visibly corroded and in fact a few were cracked - one flaked to bits at the slightest touch, so I've had the wheel rebuilt with brass nipples and CX-Ray spokes and bearings all replaced as well. All feels perfect and runs quietly and smoothly, finally! So, sounds like the issue was any of the spokes, corroding nipples or worn bearings - can't tell which but glad to have sorted it!
On other news, was putting it all back together and noticed the surface finish of the not that old Ultegra Di2 rear mech is flaking off and looks corroded underneath, so next thing to sort isn't far behind, depressingly enough...