Tried to find the sound online and on Youtube, but no luck. Listened to a bunch of sounds!
Listening to animals in the wild has convinced me that many species make a much wider variety of sounds than we know about. We are perhaps famiiar with their main mating sounds etc. but over my years afield, many have surprised me by making sounds I had no idea that kind of critter could make.
Heard a cougar sound like an owl, a black bear moan and whine and wail much like a whale song, coyotes make so many sounds I can't keep track, lynx that sound like a cow moose in heat, and then like a mule deer doe snorting at me. Am still curious about the recent belch in the woods, and about a few others...