disengaged? or only while your letting it out? if its the latter, Many high-performance clutches (inlcuding my max sport/street) have a habit of shuddering ( I believe this is what Greg @ specialtyZ called it) something related with the friction material being so "grabby" that it kind of grabs-releases-grabs-releases instead of just sliding on the flywheel during disengagement. This does make an audible shuddering sound and it can be felt slightly through the car