I had the same problem turned out to be a the abs wire/sensor. A quick and easy way to make sure it is the ABS is to pull the ABS fuse. The ABS light on the dash will come on, but if the problem goes away you've definetly determined the problem is in the ABS. One down side is I couldn't find a store who would sell just the wire/sensor. It comes as a set with the hub. Fortunately for me I had replaced the hub a while back and had a lifetime warranty.
Good luck