My money is on the clutch pedal pivot, where the spring hooks over the stay, or the clutch (electric sensor) switch. Give them a squirt of WD40, if the sound seems to be coming from inside the car... If that works for a while, then put a tiny blob of grease in the same place (spring hooks and stay, don't grease the switch) as it'll last longer.
Otherwise, the only other moving part that is unlubricated is the slave cylinder rod, where it presses into what should be a nylon cup in the clutch release arm.
Ralf S.