Hi Dan,

Thanks for the suggestion.

Actually, I spent the whole of yesterday evening (til 2am!) removing everything that I thought might be implicated (cassette, chain, pedals, cranks, chainrings, BB unit), degreased and cleaned them all, then regreased, reassembled, etc. I also took the opportunity to check the frame close up for signs of cracks/weak points. Everything seemed OK, except ....

.... the locking/retaining nuts in the chainrings (the ones that hold the chainrings together and hold them on to the 'spider') had worked loose. VERY loose. One nut was so loose it was within half a turn of falling out. This hadn't been apparent when everything was on the bike during my rides Sunday and yesterday. I guess the tension of the chain etc. gave the illusion of them being rigid during my many confused roadside checks. That's almost certainly the problem. I'm about to do my commute to work now so will see how it is and report back.

Searching the various forums and blogs yesterday (including this fine one) gave me many things to consider as a source of the pinging, based on the experience of others - chain about to snap, frame cracks, loose seat, loose headset, BB problems, pedal bearings worn, etc etc. - but no one mentioned the chainring retainers.

I've not had these cranks/chainrings long (Stronglight 50/34 compact). Just goes to show how easy it is to overlook certain things during regular bike checks/maintenance, and how easy it is to take the quality of new components for granted. From now on I'll have a new item on my checklist: "Remove chain from chainrings and check tighness of chainring retainer nuts"!

I'll let you know later today if I've really solved the problem.

Best regards,
Neil