Greetings, all -

I am beset by an unidentifiable (by me, anyway) noise from my rear wheel - a rhythmic pinging that sounds with every revolution. It sounds like something plucking a spoke, but I can't see anything that would be doing so. And why only once per rev? Could it have something to do with spoke tension? Something inside the rim? Wheel is older, 36-hole Campy hub, on an early 90s Ritchey Road Classic. I await your wisdom and thank you in advance,

Bob