Interesting. Mine was only doing it when the car hit those rpms with the clutch engaged (ie. fully extended up with foot not on it) in nuetral. I don't think it's a function of a clutch problem as much as it is a lightweight flywheel at low rpms. By engaging at that low of an rpm, you could be bogging down the engine as well. Are you getting any other symptoms?
You could have dried boots, but it's not directly related to the clutch itself.