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Some progress. The noise is down to a gentle rattle now. Things that helped were:
Positioning teeth in the middle of the chain rollers by experimenting with a different width spacer along rear wheel axle. What I originally thought was a perfect chainline was still about 2mm out. This was increasing noise as it moved against the inside plates of the chain.
Backing off the tension of the chain at the tightest point and giving it some slack.
Using a 3/32 sprocket.
Large dose of Finish Line on the inside of the chain rollers.I also learned about chordal action along the way which turns chain friction at certain speeds into vibration. A higher tooth count on the sprocket (16 to 18) has helped a lot with this. So I don't think it was a single problem, more combination of lots of factors.
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Drop looks big between saddle and bars. Unslamming stem might help relieve pressure and solve saddle issues?
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Ritte reep?
Masi.
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The Izumi Standard Track chain came today and fitting it reduced the noise from the 1Z1 chain. The profile of it seems beefier, thicker plates than 1Z1 and excellent sticky lube was already applied. There was still friction though. Scilly, you were right about this:
The vibration is coming from the "chain suck": as the chain pings off the teeth it vibrates.
Looking close up and moving the pedals slowly I can see the square teeth of the Planet X cog is hanging on to the chain, like it is catching. Then it is dropping off, this (I think) is causing the sound at higher revolutions. I had a play around with shifting chain line around; sitting the wheel on top of the dropouts with the bike upside down. I got the chain line damn-near perfect. The chainring and cog teeth were sat bang in the centre of the chain plates. and still sound, and the chain suck. Conclusion is that it has to be the sprocket, the carbon frame is acting as a loudspeaker to whatever vertical friction is happening there. So now i am looking at getting a sprocket with a more pointy profile to the teeth and a shinier finish. My chainring has pointy teeth and no such chain suck is happening there, so I'm hoping that will solve the problem.
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It was around £20 from memory, I had a few things done at once. They aren't the cheapest, of course. I had no clear sign on my forks that they had been in a smash though, so I was a bit more comfortable with sorting them out.
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Your pictures show an almost identical situation. I had, 531 forks too. I'd say give it a go, especially if you have the tools. However it is a risk and down to your own peace of mind, for the cost of a set of used 531 forks. For what it is worth, Mercian turned it around with no bother.
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I had something very similar repaired by Mercian recently. It was fine. Obviously if you have evidence that it has been in a smash then go over the frame and forks in detail to check for any more serious damage.
Here.