Above gives good tips about cracked reluctor ring or loose axle shaft center bolt (behind the wheel center cap, just pop out the cap). Also I once had to remove the abs sensor from the wheel spindle and after undoing the small retaining bolt, I pulled on the wire to remove the sensor itself. The sensor usually gets stuck in its hole and I later on realized that pulling on its wire even so slightly, it damages it internally without any visual hint. I recommend always popping out the sensor using a flat screw driver from underneath, in between the sensor and the reluctor ring. When my sensor went bad, I would get and SRS message after the car runs the abs test - usually as you drive off when it changes from 1st to 2nd gear, it usually also makes a faint 'springy' sound.
https://youtu.be/wg1XKQS6fdA