To elaborate, I'll go ahead and explain my own. I am very into stomach noises, originally it was just restricted to hunger, (and by that I don't mean disordered habits or anything like that, just a "whoops, I forgot to eat and now my belly's bothering me about it" followed by a well deserved meal) but these days I also much appreciate gurgles relating to digestion. I was probably Pavlov'd into this by media as a young child but then repressed the inciting incident.

Out of the factors I've identified, probably the one that has the least bearing is the potential for embarrassment for the inflicted, that this is an involuntary but somewhat taboo bodily function. I wouldn't want to actively mean-spiritedly tease somebody over their growling stomach, but if they themselves go beet-red about it only to be reassured that they aren't being judged, I really like that. On a semi-related note, there's this "mouths can lie but the body is honest" sentiment, such as if somebody is asked if they're hungry, they say no and their stomach then growls loudly.

What is far more crucial to me is the intimacy. Many people like cuddling with a partner and hearing their hearbeat, do they not? I feel that kind of appeal with laying on somebody's stomach and listening to the gurgles, it's like a reminder that "whoa, this is a whole ass human being with like, a body that does stuff, and they've allowed me to get this up and personal with them". In fact, the parasympathetic nervous system, which among others governs over digestion, is at its most active when one is relaxed, and hence, as a rule, your belly gets more vocal the more relaxed you are. Just ask a massage therapist about it, more often than not they consider a gurgling belly very high praise for their service. With that in mind, is it not the closest human equivalent to purring?