Hi @sandronardi
Could be a sticking or faulty [https://www.amazon.com.au/Module-iRobot-Roomba-Cleaner-Replacement/dp/B0BC46MBDX|side brush motor] (example only).
Here's a [https://www.youtube.com/watch?v=hOZWmf7BTBE|video] that may help.
Read some of the comments below the video as to what some of the problems with the side brush motor can be.
If the motor is faulty, replacements are available online. Search for ''Roomba 500 series side brush motor'' to find suppliers that suit you best.