Spouse randomly makes a distressed “aaahh” type of anxious vocalization/grunt, especially when upset or anxious. What could this be?

He has PTSD from terrible military trauma and I don’t know if it’s related to that, or what is causing it. He has some control over it (in that he won’t just randomly do it in public) but otherwise it seems very compulsive. I especially notice when he showers or is alone in a room and anxious, and he can do it multiple times in a short timespan. If he’s really upset it will be a swearword in the same “aaaahhh” strained manner. Thoughts?