There's nothing silent about it! Prior to entering turbulance there's normally a 'bing bong' when the seatbelt signs illuminate but unfortunately not all of the pax take any notice and the cabin crew do nothing to stop someone going to the lav while these mandatory signs are on. I bet that a very high percentage of aircrew follow their own advise of wearing their seatbelt even when the signs are off, it's a different percentage with the SLF.