I'm still awaiting a female view as I'm convinced it is the sigh of a contented [well serviced] fanny ...
Maybe like a bloke who farts and belches when he's had his fill of curry and beer, kinda thing.
Per the earlier responses, the clip of he "lady" who could "botty-burp" 90-odd times in 30...
I'm intrigued by this phenomena
Obviously a natural bodily function [it can't be done on demand], but like other escapes of air, usually a source of embarrassment, often met with giggles and apologies ...
I'd like to think it's the fanny saying it's had a jolly good time and has had its "fill"...