I have a gorgeous 15 month old sprocker/beagle mix and I wondered if anyone else’s dog does the same as mine. When he’s been snoozing, either overnight or if we’ve popped out (so he’s been alone for a bit), and one of us comes in to see him, he will wag his tail, roll on his back and make a low rumbling growling sound. He’s always done it, so nothing new, but is getting more frequent recently. At first we thought it meant he wasn’t happy, so we backed off, but over time it seems that he is actually happy to see us and wants petting (he has relaxed body language and waggy tail), so I’m wondering if it’s like a cat purring and it’s just his way of letting us know he’s happy? I’ve never heard a dog do this before!
Just to add, it’s not that we go and wake him up, he will look at us, and either come over to us or roll on his back for a belly rub and wag his tail when he’s making the rumbling noise. I can’t really describe it well, but not a snarl or play growl, it’s lower and longer.