Before it went dark I pulled the wheel off - nothing trapped in the caliper or dust shield, only a tiny amount of runout in the disc, caliper is in decent condition and holding the pads well. I’ve cleaned it up and removed some rust and no difference.
I can’t spin the wheel quick enough to make the noise - but I did roll the wheel over and scrutinise the tread - I can’t see any bulges, nails or the like. The tyre and the rim run true too - in both axis.
So many suggestions around the tyre though that I think my next step is to swap the back tyres from side to side and see if the noise moves. The tyres have already been moved onto other rims - and I don’t think the same tyre ended up back on that corner … but I’ll check.
After they - I think it’s putting it on stands.