I'd say that you have a dry spindle bushing. The ABS sensor works on detecting pulses from an encoder on the Birfield. A real bad session would cause a lot of vibration and mess up that signal, possibly enough to creat a warning lamp.
FWIW, I still have the recording of my bushing noise. pm me with an e-mail address and I'll send it off. The recording is a 15second one of a particularly bad session. Unmistakable, believe me!