From Yellowstone National Park:

Grizzly bears sometimes vocalize when agitated or nervous. These sounds of huffing, jaw-popping, and low growls are warnings: back away and give the bear more space.

You must stay at least 100 yards/91 meters away from bears. This recording was made on an LG Android phone by grizzly bear scientists working in the park.

If you plan on spending time outdoors in Montana this summer, make sure that you are bear aware. Always carry bear spray, and bear-proof your campsite.