Rarely do I hoot, but when I do it's with my natural voice.  The property I have hunted (up until this year 

) if you hooted, you wouldn't hear a thing all morning, within earshot of where you hooted.  I guess they had been messed with so much, they wouldn't respond to it.  Or it could have also been the preditor #'s on the property, because you may as well wait until the crows started sounding off before listening for a gobble.  They stay quiet until the sun is up and they can see the ground.