Rubber continuously variable transmission (CVT) belts are extensively applied in automotive industry. The tones of belt 'whistle' noise, which vary with belt transmission speed during low- and high-ratio operations, annoy drivers, especially when the throttle is closed and the vehicle is in motoring condition. In this study, two types of scooters with different cylinder volumes are taken as examples to cope with this problem for reducing belt noise. In the investigation, the varying order of CVT belt noise based on engine revolution speed can be exactly tracked. Thus the whistle-like noise can be confirmatively identified as CVT belt noise. Some design parameters of the CVT-belt and -structure, which influence the radiation of this annoying noise, are examined as well. To suppress CVT belt noise, some useful design modifications are made and justified.