WHen I pressed the brakes going over 40mph, my brakes vibnrated, sounding like a playing card on the spokes of a bike. I had my rotors replaced and the sound has diminished, but I just drove it at at 40 MPH, i hear the sound when the car slows to about 20 MPH. its much fainter, but stillt there. THe break pads were put on about 1000 miles ago *(before I replaced the rotors). can the pads cause the sound? should they replace the pads? What else could cause that "playing card in the spokes" sound when I brake at speeds of 40+ mph?