Why do dogs grunt?

Answer 1

It is more then likely a form of communication. Dogs grunt when they are situating themselves for naps, have to go to the bathroom outside, getting scratched or belly rubs. They communicate in this manner for many reasons but more likely for pleasurable ones.

Answer 2

Dogs may grunt as a way to communicate their emotions or needs, such as contentment, excitement, frustration, or discomfort. Grunting can also be a physical response to exertion, like when they are stretching or trying to move heavy objects. Each dog is unique, so the reasons for grunting can vary.