Your brake problem is most likely from warped rotors either front or rear. The front is more common because they generate more heat, it can also be caused my not torqueing the lug bolts to the correct torque {air gun}. the brake rotors can be checked on the car with the wheels removed using a dial indicator to measure excessive runnout about .004 will start to cause some excessive vibration. It's not the pads and having your diagnostic codes for the abs will be a waste of your money. Volvo sells a silencing pad that is installed behind the rear pad to improve anti squeal it helps, and on your model the factory pads are the quietest, we have stopped using repco, pbr and ferrodo on this model do to customer noise complaint. All of these pads wear better than OE VOLVO but we had to many complaints of noise or vibration (not pulsation).

Have your mechanic measure your rotors for excessive runnout.