I have a knocking noise that has developed recently while pedaling seated. It does not happen when I'm out of the saddle. I've narrowed it down to a saddle/seatpost noise but have been unable to eliminate the knock. I removed the saddle and lubricated the bolts and rails to no avail. My bike is carbon and the post is aluminum. I put my old carbon post back on and noticed that the noise was reduced dramatically however would still occur from time to time (not with every pedal stroke like with the aluminum post). Does anyone have any suggestions? I'm thinking that the fit is not as tight with the alloy post which may be causing the knocking noise.