Outer Limits 4x4 Board

I have a 96 v6 vitara and whilst resealing the sump I found the front diff didn't have any vacuum pump lines going to it.I thought all V6 vits had a vacuum operated engagement,as I had the auto hub as well (changed them to manual as i don't trust them.)
Also when ignition is first turned on or off I can hear a buzz type sound at front of car which sounds like a pump.
Vehicle was purchased second hand drives fine offroad-no drive line wind up.