I don't know a whole lot about bikes, but I've been trying to learn. I have a Cannondale CAAD9 and lately I've been having some troubles with the derailleur and shifting. The most recent problem: when I start pedaling, the bike clicks and rides really choppy. It feels like it's trying to shift gears when I'm not shifting and clicks a lot. This is only a problem when I'm riding- I've set it up and tried to adjust the cable tension and then it seems fine, but when I start riding it, it acts up again.
Apologies for my limited knowledge about the problem- I wish I could describe it better than this but any input is greatly appreciated!
Step 1: remove the rear wheel and ensure that the cassette is installed tightly. You should not be able to wiggle it at all.
Step 2: reinstall wheel and ensure that axle is fully resting in dropouts and skewer is properly tightened.
Step 3: If after eliminating 1 & 2 and a Test Ride, the problem persists, inspect frame for cracks/ broken welds/ etc that might induce flex in the rear triangle. Actually - do this First.
First Law of Bicycle Mechanics - "Just because it works in the repair stand doesn't mean it works".
Wheelies don't pop themselves. (from a QBP fortune cookie)
I actually prefer to set the final cable tension on the road making only minor changes (needs like half a turn or so) and then going through the whole cassette range twice and carefully listen and feel for misshifts. Do this on a farm road somewhere away from any traffic, though. You will not be concentrated on anything but the shifting!
And also check that the cables are ok. This actually was the reason for my road bike to misbehave. I always tell people to check that often, but as always the guy advertising this is not the one who is doing it. Was a face-palm-worthy moment. However, frayed cables and weak springs usually show up on the repair stand, too.
Check that your chainring bolts are tight!
[font=Trebuchet MS][size=x-small][color=#FF0000]At my age it's the knees that creak.[/color][/size][/font]