Today, over a year after the problem started I have managed to find time to look into this problem.
I have not put it all back together as I have had to order a starlock washer but this is my guess at the problem.
The door strap is held into a bracket that is bolted to the inside of the door by a pin. The pin has a starlock washer on the bottom. My washer had fallen down allowing the pin to rise. The pin goes through a roller, the door strap fits between two rollers.
The pin had risen enough to have come out of the bottom hole of the bracket and each time the door was opened and closed the pin with the roller would tilt. I think this is what was making the noise.
I am not using the same Starlock washer and am fitting new one. The pin is, it seems, hardened and so drilling and putting a split pin in has not been possible.
Here is a link to the starlock washer, 5mm is required, pin seems to be 5.18mm diameter
https://www.spaldingfasteners.co.uk/...2-4mm-to-24mm/
macafee2