Rudder Trims....
We had a fleet of 23 737-200s and all except one, required right rudder trim in climb, some in cruise and none in descent. We had a close relationship with the engineering guys and the rigging department was sure that the trims were set to neutral.
We are taught to believe that there is no torque on jet engines, but considering this discussion isn't a 'one off', maybe there is some credibility in it. We used to toss this one around over a coffee and in the bar a lot and we all felt that considering the amount of power/weight generated, torque did have an influence.