Bicycle Mechanics - Assessing and Diagnosing Drive Train Noise

I must admit as functionally intimate as my relationship to my bike is - it is like an organic extension continuous with my body - I am ignorant, dumb when it comes to figuring out mechanical malfunction. So dumb, I am embarrassed to take it to the mechanic or even post in this anonymous mechanics forum. It is somewhat anomalous,weird because I am quite good at assessing and diagnosing in my professional life.

Anyway, abashed preamble aside - I have a Campy Record double set up. I am getting what seems to be, sounds like chain rub - especially noticeable when I am on the large chain ring and in the middle range of the cassette. However, when I am off the bike and spin the crank hard I do not see any chain contact or hear the noise. The shifting efficacy is unimpaired. I swear I cannot say if it is coming from the back or the front! :o

Any ideas to give me a clue?

Always difficult to trace where noise is coming from when on the bike. When the chain is under stress it may be rubbing and you might not see this with the bike on a stand.

http://www.sheldonbrown.com/creaks.html

I run a Campy Record 10 on a carbon frame and worked out any noise myself. Sometimes a carbon frame amplifies any little drivetrain noise.

First, to check the front derailleur, ride in a flat open area, put it in the gear in question and apply real pressure to the pedals. Watch the crank to see if it flexes in the frame at all. Sometimes, if your frame is not super stiff, the frame will flex enough to allow the chain to rub on the fornt derailleur when under pressure. If this is the case, make sure your bottom bracket is tight enough, if it is the flex is in the frame but there is nothing you can do about it. Center the front derailleur over where the chain is running to avoid this.

If it could be rear like mine was, I put the bike in a stand, shifted into the noisy gear, dead center. I scrutinized the position of the chain out of the derailleur to the gear. Is the chain sitting dead center on the cog or is it on one side or the other? Play with your barrel adjuster just a bit to center it and see if that does not shut it up.