Do not remove those knobs. Ask me how I know. What is making your noise could be two things or more. One could be the motor bearing. Put a little drop of oil on the shaft. The other thing could be it needs oil under the bobbin holder and under that. I had one one time gave me fits until I oiled that area real good and ran it a bit. I have a rip roaring ear infection or I would do some photos. Maybe someone knows what I mean and can add to this.