For me, a random burp regardless of quality doesn’t do much for me personally. What turns me on is when I hear the second burp, realize the burps are deliberately done on command with gulped and/or I haled air, and the belcher can do it when we and as many times as desired. When I realize that is the case, I get indescribably horny.
What about you? When does your fetish get triggered?
I get aroused pretty indiscriminately lol. It’s so hot hearing or seeing someone burp deliberately, especially if it’s loud and rude and the tone is gross 
but I also find natural, accidental or uncontrollable burps to be really hot. Especially if someone’s actually trying to stifle them but can’t, or keeps apologizing, etc. It’s all so hot to me 
Mine gets triggered if the burp sounds natural and not forced. That’s all I really want, as they are true burps. Listening to loud forced burps does nothing for me. The bodily function itself is more fascinating to me than how loud someone can do it. The more natural it sounds, the more I like it.
A bit like when you’re full after a big meal and you uncontrollably do a belch, no force whatsoever but the belch still felt good and relieving.