How to rid the IKEA MARKUS of squeaking
1. Remove the seat from the chair with a 6-sided metal tool (size 5). It's connected with 4 bolts. Putting the chair upside-down on a table for this makes it easier.
2. Put the chair back on the floor and put some newspapers under it.
3. Get a can of general use silicon spray or teflon spray
4. Spray on all connecting parts that you can reach on the inside and outside of the metal base. Make sure you get the 4 points, one of which is highligted in green underneath, because that's where most of the noise comes from. Spray from the outside as well as sideways between the metal and the inside.
5. Test if all the noise is removed by putting your weight with two hands on the metal base and move from side to side. If there is still noise, you missed a spot.
6. Make sure there is no leftover spray that gets on your floor, as you turn the seat back around. Just use some toilet paper to remove if you see any.
7. Put the seat back on. And you're done.
A piece of steel was fractured in mine, but it didn't appear to be a problem. But certainly something to look out for in case of long term use (years) to prevent accidents.