interference with PWM drivers coupled to the PFC as load

I have an independent PFC front end for giving full range 80VAC to 270AC input from mains at 500watts level.The frequency used by me is 65KHz.
I used the 375VDC developed to drive a PWM switch in flyback mode and found interference of 70KHz with my 120KHz ....increase to 168KHz still had the intereference disturbance on the PWM...
guidance required on how to get rid of this ....