E36 Brake Question

[prariepilot]

I've upgraded the brakes on my 1999 318ti M44 to drilled and slotted disks and ceramic brake pads. Now, there is a very low speed "abs chatter" that occurs below five mph regardless of how hard the braking is from speed. I can be running sixty and step on the brake - not hard, but firm. The "chatter doesn't start until I'm almost completely stopped.
Is there a "left" and "right" designated rotor when using slotted and drilled disks? Might this be causing the "chatter" if installed backwards? I'm not getting any codes from the OBDII, so I don't suspect a wheel speed sensor. Thanks for any suggestions.