Hello hotdog, my name is Kevin and I work in Workspaces for IKEA
Woodbridge
.
The knob on the bottom of the chair (egg shaped) is the tilt tension knob. If you turn this knob to the left or right it increases or decreases the amount of force you need to apply to the back of the chair to go back in it. More tension and you have to push harder to lean back.
The metal grinding sound is not normal behavior. I am sitting in my Markus right now and I don't seem to have that issue. If it's a real problem, disassemble the chair and take it back to your local IKEA along with the receipt and have them swap it out for another one. That's very unusual for Markus to have a defect, they are one of our best chairs.
Kevin
Workspaces - IKEA Woodbridge