I have a shifting problem.

The bike has a 9 speed drivetrain with low miles. The fd/rd/crankset are Ultegra 6500. It is a triple crankset. The rd cable is new. The shifter is a 7700 bar end.

When I have the bike in the middle ring, and I pedal hard (like standing up), the chain skips on to the small ring on the crankset. The problem has gotten worse over time, so that I can reproduce it fairly easily now. The chain does not skip when it is on the largest (outer) chainring.

I am trying to diagnose what the problem is. The list of potential causes is:

• Bent chain
• fd adjusted improperly
• bent chainring
• crud in the chainring
• loose chainring
• loose crankarm

In addition to these causes, what are the other ones that I need to look for?