When cycling my road bike, if there's a little pressure such as going up a hill, or putting a bit more whoomf down than normal, there's a knocking of metal on metal, which I think is comeing from my left crank. In fact I initially thought it was a loose strap clanking on my seat stem. It doesn't seem to have any effect on my power output, but the clanking annoys the heck out of me and my mate. I'm worried that some bearings inside the hub (?) are being chewed up, but it not a grating, just a clunk. Sorry to be so technical and precise. (not)