You said that you opened up the print head and saw major wear on it. Was just pointing out a source that had it in stock. It could be that the tension upgrade is not aligned correctly causing the noise. You could swap the gear from the newer machine to see if it makes a difference or at least compare the tooth depth between the two. It could also be the bearing and not the gear that is making the noise or even the drive servo. Unload the filament and run a load cycle without filament and see if the noise is still there. If it is look at the bearing or servo.