I spooked some hogs this year. When they ran off they were making a grunt that sounded like a dog barking. A very deep and aggresive noise.But never heard a growl.

It is actually an alert call to other pigs. In hog it means haul ass

I may be wrong about your answer Scott but this hog was not spooked.  He may have been telling the boar scent he smelled to leave, but he was within 5 or 6 feet from me and growling the whole time, for at least 3 minutes.  Then he grunted and walked off.

I KNOW WHAT YOUR TALKING ABOUT.. LAST YEAR WHILE WALKING TO BY BOW STAND IN DARKNESS EARLY MORNING, WHEN I START GETTING CLOSE TO MY TRIPOD I CAN HEAR HOGS AT MY FEEDER ALREADY BUT YOU HAVE TO PASS BY FEEDER AT ABOUT 15 YARDS. AT THIS POINT I DONT KNOW IF I SHOULD JUST WAIT FOR DAY BREAK OR TRY AND SNEAK PAST THEM HOGS. I COULD HEAR THEM FIGHTING FOR CORN.. I DECIDED I WAS GOING TO TRY AND SNEAK BY THEM. AS SOON AS I COULD SEE MY PINS I LET A MUZZY FLY. I HIT A MID SIZE SOW TOOK OUT BOTH SHOULDERS  SHE DROPED IN HER TACKS. THERE WAS A BIG BOAR RUNNING AROUND GROWLING AND MAKING ALL THESE CRAZY NOISES HE WAS PISSED OFF AND HE WANTED TO KNOW JUST KILLED HIS MATE. I WANTED TO PUT AN ARROW IN HIM BUT COULDNT GET CLEAR SHOT...

MATHEWS DXT  

Stoxbowhunter, I'm glad someone else has heard this.  You can appreciate my feelings hearing this in the dark just feet from me in a small tent blind.  It made my little ground blind part of my junk pile. Last weekend I dropped a 265 & 185 lb. boar under the same feeder (from a tree stand, 135 yds. from the feeder).

It's a hogdog.