Not sure about your scooter, but I had a Holden Commodore that used to do that from new, eventually (after about 10 months of my bitching) GMH came up with some spring shims that fitted between the brake pad and disc brake piston.
Apparently on the Holden, the awful squeaking noise was actually caused by the disc brake pad vibrating !!
EDIT:
Another thought, I have a feeling there is also a "grease" type material on the market to stop that noise, that you wipe over the back plate of the disc pad, the part that is in contact with the disc brake piston, NOT the side that faces the disc rotor, might be worth a visit to check out your local Repco store....