It sounds like worn brake pads. The brake pads have a small metal clip that protrude from the side and when they are worn they come in contact with the rotor which produces the sound that you described.
When it starts cracking(squeaking).
It's a Saturn..
Saturn
It probably wants something like food or new bedding. It may be in pain. If not it is probably just squeaking. I mean not even WE can be mute forever!
Unless I'm mistaken, Saturn is the ringy thingy.
Saturn ion
Saturn
Saturn
If your guinea pig starts to get crusty eyes or isn't squeaking take it to the vet!
I would take it to the vet if you are worried. It might be in pain from some sort of illness.
metal starts squeaking when it touches the dryice because the metal is warmer than the dryice
Normally when the child is 18, or starts work.