He made a wierd noise, confused me greatly!! please help!! (Easy 10 points)!?

so i hugged this guy who ive been crushin on, we stopped, and then he pulled me back in for a second one. on this one, he made sort of a gruntish like sound, like a Mmmm sound. it just kinda confused me, lol, he does this sometimes when we hug, and he will also kiss my head sometimes. what does it mean, please?