I can feel the stutter of my ABS brakes at a low braking speed?

I can feel the stutter of my ABS brakes at a low braking speed. This is an intermittent problem. I also hear the hum or whine of the ABS system, or what I think is the ABS system, when I'm not braking - but usually when going slowly.

Could the sensor be going bad? Any suggestions of things to look for to check out this problem?

Thanks soooo much for any help!