This is a question that we often get from sitter and owners who work with Rover. Help the community out by answering them in our forum!
I have a dog I pet sit that grunts and/or sighs when she lays down at the end of a busy active day or when we go to bed. So Funny! If a dog grunts as you approach (s)he could simply be giving you a hello. When I approach this particular pup, she will grunt and roll over for a belly rub. Sometimes she gives a soft grunt in her sleep and can be dreaming. But, it can ALSO be a sign of a respiratory or abdominal issue so observe the dog(s) normality and take it seriously if it seems out of characteristic for him/her.