I thought the same thing when I felt a shudder from the clutch pedal with my foot just touching it. Turns out my car that some vibration comes throught the clutch pedal with no pressure applied. If you put any pressure on the pedal then it goes away so it is not a mechanical problem but appears to be a harmonic issue that occasionally shakes the pedal. Anyway, I've stopped worrying and accepted it as a characteristic of the car.
Hope this helps
