Recently purchased a second 93 850 for my daughter to drive to school. One week after purchase I had to have extensive brake work, front and back. Right after this was done I noticed on occasion when I apply the brake it makes a weird noise and the brake pedal pulls back toward me. This happens at low speeds, on dry pavement and often when applying the brakes on a left turn. The car has been at the dealer now for three weeks and of course does not misbehave for them. According to the mechanic they did get a code to come up on the wheel sensors, all four of them. He also said it was highly unlikely that all four sensors would be bad at one time. The ABS light comes on only during start up as it should and not when the brakes act up. Any suggestions ???