he was dug out in 4:28 after the avalanche happens, which is ridiculously fast. the sound he was making was him struggling to breathe becasue the avalung was knocked away from his mouth, so he only had it half in his mouth. some of the noise is also his chest moving up and down from breathing so hard.
and it is like digging through concrete to get out. think about shoveling the driveway when it has a foot of snow on it, only about five times as much snow and having to do it with one arm at a time.