grinding/vibration from engine at lows revs vrs

Hey guys, over the past few days my car has found itself an in gear low rev (less than 1500rpm) grinding/vibrating noise :( there doesnt seem to be any vibration coming back through cabin either. It also doesnt seem to happen when the clutch is disengaged and the engine is revved, its only when the engine is in gear and around 1300rpm so i cant seem to work out if its the flywheel or clutch or both :( the clutch has been slipping for a while and is being changed next week so hopefully this will cure it?? can anyone part any wisdom?? thanks