This 2009 thread still pops up first in a google search for €œhow to silence noisy doorknob,€� but all the answers suck. The internet has failed you.

If you still have a loud doorknob...after these 9 years...just wrap a rubber band tightly around the cylinder, stretching it up into the crack between the knob and door, and keep winding until you run out of band. Should be hidden too. Use another one on the other side as well, if necessary.

I hope your wifes sleep hasnt suffered too much over the past decade!