I've had the same problem in my '95 Sunfire, but it's very intermittent and normally doesn't happen at all. It seemed to happen more frequently in the winter time (go figure), and I ended up pulling the fuse for a while. Anyways, when the ABS does freak out it's normally at low speeds, like while rounding a corner, and sometimes I can hear it clattering when I hit a hard bump. I haven't looked into it at all, and frankly ABS scares the shit out of me when it happens in the winter time.
I'm used to pumping the brakes.