Swift, that is completely normal for the Mega motors. See Megas are six pole motors and Hackers are two pole motors. What this mean is that the rotor has either 2 slots or 6 slots. Take a look at the Mega Motors usa home page they can explain far better than I could or maybe someone else can explain the whole idea, but dont worry the cogging effect that you feel when you spin the motor is normal for a Mega motor.
Viper