Abs light on but not always

Depending on what car you have. It's as though you have an abs ring/sensor fault, the noise you are hearing is the abs pump working this is because the gap between the abs sensor and the abs ring is to close, which make's the abs control module think that the wheel has locked up. causing it to open the valves in the abs hydro unit to try take away the pressure from the side with the fault.

have you checked abs rings on drive shafts if broke abs will pump as its thinking its wheel is slipping you could wire brush them to see if they are broke

If you have ABS and that warning light comes on, you should have the system scanned for trouble codes. The code will point you in the right direction to look for the problem.
Could be a faulty brake caliper, or other problem.

Same proceedure, every time, any light comes on

You have an OBD2 System Malfunction

Always try and retrieve the codes,diagnose
and repair.

ABS --could be a wheel speed sensor,
or some other issues

abs light could be brake pads need replacing/sensor gone.check pads NOW...18th of an inch is too low.... radio is telling you to wait until it will take the correct code (inputted wrong the last time)

cheeck the e brake cable or brakes in the rear see if the brake in the back look funny thin cheeck the front next time you drive it slam on the baraks pritty hard and let me now if you slide like the wheels lockt up or if the wheels did not lock up but stop the vehicle

The ABS system always is engaged when the brakes are applied. If you are talking about the ABS light coming on then it is a little bit of a different story. If the light has come on at all there will always be a code stored. I would take it to a shop that has a scan tool to read ABS lights and ask them what the computer is saying. This is the only true way to get this problem fixed.

Have you checked your brake fluid? It may be low or an indication that the brake pads are worn, causing the light to stay on.

This problem sounds like and ABS module that has gone bad, the ABS module has toothed gears inside that actuate the ABS motor, if one of these gears slips a tooth or "unwinds" itself if will not circulate brake fluid to where it needs to go (ex: the rear brakes) alot of times the brake and ABS light will come on, but will not set any trouble codes. My recommendation is to take this to a repair shop and have them verify the problem and replace the ABS module, the motor gears have to be properly aligned when replacing or the lights will stay on and you will still have the same problem. Hope this helps.

the sensor by the rotter was damaged by brake pad replacement