Spotted a "New Other" Shimano rear hub on ebay on Wednesday, that looked like the one on my 29er, at £15 inc postage without original packaging.
It arrived around midday today, so I measured the hubs to verify they were similar, stripped the old hub out of the rear wheel (the wheel bearings were not in great condition when I re-balled them a few months ago, and the cassette hub bearings have been getting louder too), cleaned up the spokes, nipples and rim and rebuilt the wheel using the new hub.
No more annoying little noises when I spin the wheel now.
A very rare occasion when the total cost of the job was just the part I wanted to replace, particularly so with wheels, and 5 hours of my time!