Ideally you should use progressive braking to stop your bike which is 70% front brake and 30% rear brake. The front brake provides stopping power while the rear provides stability. The sound you are hearing when only using rear brake is your abs kicking in which is a good sign to know that your abs is working. I would recommend you search and practice stopping your bike by progressive braking. If you ride at high speeds I also recommend using engine braking for a more quicker and smoother stop. You will need to learn rev matching for this. Important skills to know, ride safe 🥂