"The real purpose of scientific method is to make sure Nature hasn't misled you into thinking you know something you don't actually know" - Robert Persig, Zen and the Art of Motorcycle Maintenance.
I was convinced the bottom bracket on my Airbourne was giving up. This was disappointing because it was a Campag Centaur with only 3000 klimotres on it.
The symptoms was an intermittant tick/rumble when pushing hard on the cranks when climbing a hill. It didn't happen when I stood up on the pedals.
It got worse and worse until it happened on every pedal stroke, and even on the slightest gradient. It didn't do it when the bike was under no load so I couldn't get it to happen on the bike stand.
The sound definitely seemed to come from the bottom bracket.
And because it occurred when pushing hard on the cranks, and not when coasting or cruising on the flat, I was sure it was the BB.
I shelled out for a new botom bracket and tool to remove it. Did the replace and stripped and cleaned up the chainrings while I was at it. The old BB was rusty on the outside and had a slight "notchy" feel. I was convinced I'd cured the problem.
Imagine my dissapointment to find no change.
Further investigation reveals the fault to be with the saddle!! (or perhaps seat post) I can get the same tick without pedalling and just rocking back and forward on the saddle!
When I climb hills in the saddle I must be shifting my position on the saddle slightly, and rocking too, whereas cruising I must use a more balanced "circular" pedalling motion.