What could cause a squeaking noise when you press the clutch, but in comes from outside, not inside the cabin?

So I rolled the windows down driving home last night, and I noticed that it sounded like my clutch pedal was squeaking. When I rolled them back up the noise went away.

So I’m assuming it’s not the pedal itself, but the slave cylinder or fork thingy.

Is it a sign of a potentially serious issue or no? Because if it’s just a squeak and nothing more, I probably won’t bother with it, but I’d like to know if it could somehow be a precursor to clutch or slave cylinder failure.