I have a 90 GS with ABS and I had to stop suddenly because of deer, and after depressing the pedal pretty hard it seemed to lose grip of the wheels or something and had a loud grinding sound. Later I tested it again and it did it. It only happens during extreme stopping. What could this be?
Your calipers could be locking and eating through your rotors. Happened to me. Have it checked NOW. You will be glad you did.
Have a shop check your brakes & calipers, maybe your pads are running out? 
Otherwise just hit the deer. :shy:
That sounds like normal ABS to me.