Interior fan pulsating up and down

[regeli]

Recently bought a Polo 1.2 TSI 2012 model and noticed this week something strange with the interior fan.
Normally the climate control is set to AUTO and AC ON. After cold start of the car and when starting to drive, I've noticed that the heater fan is pulsating up and down.
I then turned OFF the AC and set the fan to full speed, the fan is then going at full speed for a second then goes down again. The fan is repeating this rest of the car trip.
Another day, I can set the fan is at full speed without pulsating up and down. But for next day, same issue again...

Anyone experienced similar issue?