If you can hear the brake grinding noise while driving it mean the pads are rubbing against the rotors. As for if you need both or just pads, It will depend on how long it has been going on and how much pressure the pads putting against the rotors.
Typically when this happens ideally both should be changed. As there are likely some groves in the rotors from the pads grinding against it.
You will have to measure the rotors thickness to know if they are still with in specification.
If they are then they need to be resurfaced. Which can be done at any of your local auto parts store.
Another thing to remember if the brakes are grinding without you applying the brake it means that you possibly have a stuck caliper, could be due to a collapsed brake hose. So if that is the case then the caliper(s) and brake hose(s) to the caliper need to be changed as well. Otherwise the brakes will still grind after replacement.
I have attached diagrams for your reference.
Please let me know of any questions.
Images (Click to enlarge)
Thursday, September 2nd, 2021 AT 7:49 PM