CD70 (whether its Dream, or CHonda), doesn't have a smooth gear box. So whatever RPM you choose for next gear, its definitely going to produce a "TUCK" sound. Also, don't pay attention to the meter reading about gears because they are false.
Its a CD70, so just make sure not to stress gears. Whenver you feel the RPMs are rising to a 'screaming level', shift to next gear.