BMW 135i scraping sound whilst reversing.

I recently bought a 135i. 22 plate, low mileage, over 50% left on breaks etc. SOMETIMES when I reverse it makes a scraping sound like the breaks are low. But it only happens sometimes and primary when the wheel is turned. Does anyone know what would cause this? If this is normal? I’ve read online people saying it has something to do with the auto hold break. But even with it off it sometimes happens. I just find it weird. I’ve tried many things to try pinpoint when and why exactly it happens but I can’t ever make it do the noise when I want it to. It just does it randomly sometimes