Though the bear sound we are most familiar with is the huffy roar that always accompanies scenes of a bear attack in movies like The Revenant or television shows like Yellowstone, bears are capable of making a much wider variety of sounds. Just look at this bear who scaled a tree in order to let everyone know how he felt.
This eerie noise sounds almost like a moan, and the bear repeats it several times. Bears have been known to moan when injured, but this guy doesn't seem to be injured. They can also produce a combative bellow when in the middle of a fight - but he's obviously not fighting anyone. And cubs can wail and scream if afraid or in pain, but this one's not a cub.
You might argue that the bear is distressed to find himself higher up than he intended to climb, but bears are excellent climbers and there doesn't seem to be any reason why he couldn't just climb back on down.
This Yosemite bear might have just felt like giving an impromptu recitation. It's not that hard to imagine - I think we all know someone who enjoys hearing themself speak.
Or maybe he's just asking for someone to pass him some Charmin.