My Sims keep making a moan noise

The last few times I've played, with various sim people, all quite different traits, likes/dislikes and characteristics they ALL keep letting out this weird sort of moan it's a little like there in distress/bored/irritated. I just can't figure it out for the life of me. In the past I've heard like one SIM do it rarely, with maybe real life weeks apart before I heard it again. But, let's say the past week it's been near every half hour someone does it, sometimes not the ones Im playing as. 

Struggling to explain it but it's like a gruff "huuurrhh" 🤣🤣 kind of noise 

I'm only asking as it does seem to be getting a bit constant and I have no idea what they mean by it as, as far as I can tell there's no picture above their head when they do it to indicate a reason 

Also posted on answers HQ but thought I'd ask here to :)