Originally Posted by jyewdell
Standard Deore XT front and rear derailleurs on Trek Fuel 90 (19.5 inch frame). Working fine until I installed new chain (SRAM PC 69). Shifting is smooth in all combinations. Chain runs rough throughout all gears using front middle ring (32 T) but is OK using large (44 T) or small ring (22T). Could this result from slightly bent rear derailleur?
Did you fiddle with the FD cable tension? On a triple, the position of the derailleur cage for the small and large chainring is "mostly" dictated by the FD limit screws. The middle chainring, on the other hand, is largely positioned by cable tension. When you are on the big cog on the RD and the middle chainring you should just have 1mm or so clearance between the chain and the inside of the FD cage. Increasing cable tension will bring the cage closer to the chain. Too much tension will have the chain rubbing against the inside plate of the FD cage. If it is rubbing, back off the tension until the rubbing just goes away.
That may, or may not, be your problem, but when it's only the middle chainring of a triple that has problems this is commonly the problem.