At "throttle" start-up......all rotors should be turning at approximately the same speed....two front turning in the same direction, opposite of the two rear.......the only time the rotor speeds should deviate is when you either yaw or turn during (position) rotation.....there can be a speed difference, between the front and rear rotors, when forward or reverse direction is engaged as well.
As mentioned previously at another forum we share, each ESC should (must) be calibrated seperately in order to insure duplication is not carried over from one to the other....(even though you may find the settings, in pairs, to require like settings)........make sure you have not (if applicable) changed any of the Transmitter values related to stick functions (all controls, except the throttle), should be centered and balanced, or have armed the ESC's in different sets of protocol.
I doubt the rotor blades are causing the issue, if you have installed them in the proper order (as indicated by the manufacture manual) and with any stamped ID's on the blades visually facing up.
Hope this helps a little...! <!-- / message -->