I've never heard of an elephant barking. (rimshot)
But as to the noise, a friend of mine reported being near a 24 pounder being fired at a historic fort in Canada. Everyone nearby was supposed to plug their ears and open their mouths. He didn't get his fingers in his ears in time. He said it was like getting hit in the chest with something padded and then a high pitched whine. He didn't even hear it as a boom.
I can imagine the ancient equivalent of the king's PR man exaggerating the impact of the big cannon and people happily repeating and embellishing the stories. "He was standing too near and the shock squeezed the eyes right out of his head!" "Just the wind of the ball traveling overhead knocked over a dozen draft horses!" Write your own.
I can also imagine a conversation with the original gunner that shot this thing. "People tell me you were the guy who lit off the big cannon." "Who bit off a pig banner?" "No, you shot the big gun, right? "Rot the wig bun fight?" "Never mind."
Then again, considering the sometimes dramatic failures of artillery pieces back in the day, the gunner would have to have been a brave man. At Fort Ticonderoga there is half of a bronze howitzer, split roughly lengthwise, that archeologists recovered from the lake nearby. It was the top half, and it must have traveled a few hundred feet before splashing down.