aBrake noise Lexus RX300

When I apply the breaks I get a chatter noise just before the vehicle stops. This is not every time, but more true than not. It happens when the breaks are applied gently in a typical stop. I have asked mechanics to check and they feel it is the ABS even though they can not isolate any issue with sensors etc. The breaks and rotors are new and check out fine. Since I am anticipating retirement I would rather not donate to the Lexus Dealer’s children?s college education unless it is really necessary.