Duc Daz,
What machine have you got - model/year ? Reason for asking is that I have a 749 Dark about 4 months old and it sounds like it's doing somthing similar. Although my problem occurs after I've stopped, as I pull away it sounds as though the brake calipers are not releasing properly and I get a graunching noise. I'm curious to see whether there's a theme here.
Jiminy