What do you mean by "recently"? If new rotors were put on about three months before the pulsation started they are likely Chinese rotors and have "aged" on the car. We let cast iron parts age 90 days before their final machining. Have the new rotors machined lightly and they will be fine. If the problem started right away when new rotors were installed, most commonly one is warped, but you also have to check for debris like rust and scale stuck between the rotor and hub. That often gets overlooked during normal brake service.