Knocking sound from extruder stap motor ender 3 pro

Hello,

I have a strange knocking noise from my extruder step motor. I removed the filament and run a test print the sound was still there. I am sure there is nothing wrong with hotend or nozzle.
I have ender 3 pro with skrr 1.4 turbo and tmc2208 drivers. I changed tms driver currents it also didnt help. What could be the problem ?

Please see video below.

<a href="https://www.youtube.com/watch?v=q6Aj3jdSXw8" target="_blank">https://youtu.be/q6Aj3jdSXw8