It may well be something to do with the dust shield on the disks. There’s a thin metal disk inboard of the brake disk.
Sometimes wee stone get caught between this and the disk. Sounds like you describe (and it sounds horrible). Not really doing any harm. Best to find the wheel and investigate – can probably encourage the stone out with a bit of pulling or a screwdriver.
Also – but it should take longer than 3 years – the shield could be rusted through or damaged. They eventually get weak and start to rub. By this stage they’re easy enough to pull off.
This happened on my Honda Civic. I pulled them off and it was good for another 100k miles so I don’t think they do much. Same thing happened on my Octavia last year so I’m guessing it’s quite common.