The determine shows the vacuum clutch mechanism. This sort of clutch employs the prevailing vacuum within the engine manifold to work the clutch. The vacuum clutch is made up of a reservoir, non-return valve, vacuum cylinder with piston, and solenoid valve.  Using your vehicle idling, hear for the growling noise https://clutch-plate17148.ssnblog.com/32170109/the-best-side-of-clutch-plate