I am being driven mad by a mysterious clanking noise on a Trek FX 7.7. It seems to be emanating from the left crank, though with an aluminum frame it's always a little difficult to pinpoint. The clank only happens when I'm applying torque, and not always then. It's inconsistent, but seems to be getting more and more persistent. Happens on both the large and middle chainring (I don't use the smallest, so I don't know about that one).
I've checked the bolts and nothing obvious is loose.
The bike is a 2010 model that was purchased in 2011 and then sold to me after having been used very little. I, on the other hand, have used it daily since February of this year.
If anyone has suggestions for diagnosing or eliminating, I would be grateful.
Thanks in advance,