Ok, I'm struggling to ignore the noise which I think is getting worse. I also think the amount of play in the chainring is increasing. No circlip pliers to hand so difficult to see what may be happening behind but have taken off the spider and gear housing case.
There appears to be a LOT of play in the sprag clutch bearing - is this normal?
https://file.io/YRV5XOtXQtT3
There is a bit of play on the main shaft but the bulk of the play is the big bearing. I tend to think it is completely knackered. I first noticed the noise at 190 miles and at 330 miles it is getting worse and the chainring has more movement.
@Woosh, if this is not normal, I understand the bearing needs to be pressed out and a new one pressed in.
Keen not to let it continue until something more significant breaks, like damage to the teath or the TS or something.
Edit: have tracked down some circlip pliers so I'll take off the big cog and see if there is some other part that is grinding away. With the amount of play it is quite conceivable the big gear is touching the housing under pedal load. Alternatively, a couple of degrees twist gets amplified at the far end of the chain. Either way, it's not ideal.