Been having an interesting issue on and off for the last little while with the s4.
Running slotted rotors with Hawk HPS pads.
When the car is cold, there's zero vibration under braking, more pedal pressure required, but I think that might have something to do with the pad compound.
After a long highway drive, the first few stops the brakes vibrate like the rotors are warped. After getting on the brakes a couple times, the vibration tends to go away. I've narrowed this down to the front rotors (doesn't happen when applying the e-brake at speed)
Anyone have insight on this? I'd think if the rotors were warped, the vibration would be constant.