My ABS light has been coming on and staying on, then going off regularly when driving. There has been no sqeaking when braking and everything seems to be braking ok. I have noticed a slight grumbling only a couple times at a complete stop but everything else seems ok. Also, the red BRAKE light sometimes comes on and off as well. I want to take care of this before I have a big problem. What could this be and how can I fix this myself or in the least expensive way?