I observed the same squeaking noises some while ago. I first thought it came from the gearbox or the drivebelt housing aerea.
But then I did a simple and quick test, that led me to the usual suspect. While pushing the scooter I just very gently and slightly pulled the rear brake lever. The squeaking noise vanished immediately.
Also, if you push both brake calipers a bit back against the disc, you will get temporarily some more free space between the brake pads. The squeaking noise should be gone now as well (but only temporarily).
The cleaning of the discs with a scrubby might help somewhat, but it´s probably not of long term help. For me this method didn´t really work to stop the squeaking.
So I learned to live with it. I am not pushing the scooter so often but rather ride it. And these riding noises I like better, as they are closer to a turbine sound of a 747 taking off.