That could be. I haven't went after them with a bow yet and most of them drop instantly. I did have a double-lung-and-spine once (magic bullet?) where the bear tried to run but couldn't move... went on a few seconds. Another I accidentally shot in the liver that had time to moan. Never a vocalization.
What an odd sound. Come to think of it, I did hear a sound like that way up top of a huge cut block one spring. It would moan for a few seconds every 30-60 seconds or so. It went on the whole time we were there (maybe 10-15 mins) ... thought maybe it was a dying moose but now I wonder if it was a bear.
I also make that sound when I get up and have to go to work... or the next day after I eat a couple pounds of extra hot wings.