Popping sounds

I'm 36w and 5d and once in a while I hear these popping or cracking sounds from my belly. It's usually when the baby is moving around and then I hear a "pop" like when you crack your knuckles. I know it's not me because I'm usually sitting or standing still when it happens. No pain at all and nothing I'm worried about. I was just curious if anyone else experienced this and knows what it is? I just keep picturing the baby stretching and cracking his knuckles or something haha