How to pronounce “thundering”(noun) in English

around this bend. Kristin was coming along behind us. And I was saying "this is where we are" and I was giving her some geographic marker of where we were.And right then, I heard this thundering to my left. And it was a herd of buffalo running from me. They'd winded me. And they ran straight in Kristin's direction. And they ran througha valley and could just come up the other side and run right into them. Luckily, they took the valley for cover. But they were really scared.