My rear brakes recently starting squealing and making a weird noise, so I had to open everything up to see what it was and it turned out to be the low brake pad warning indicator. It's a simple little piece of metal that is designed to make contact with the brake disc when the pads wear down low enough. If you ignore the squealing sound, it may eventually start squealing continuously, even when you're not braking.
My discs and pads were in shocking condition, so I replaced them immediately.
I hope you enjoyed watching and hope this helped you understand how this little "system" works.
