I have a 1987 300D, and lately I've noticed that when I apply the brakes, I hear a "ticking" or "clicking" noise coming from what sounds like the front driver's side of the car. It sounds like it's coming from the ABS unit. My brakes seem to operate normally, but I've not tried slamming on the brakes to see if the ABS is working. Can anyone give me some ideas of what that noise might be, and what I would need to do in order to fix it?

Thanks!

Dan