Honest cross-question!! Why do some "bottom burps" come out silent and some vastly loud and flappy sounding?

My son asked me this and I had no answer. I am in a minute really curious about the nouns / no sound issue when a being passes gas.Honest cross-question!! Why do some "bottom burps" come out silent and some vastly loud and flappy sounding?
Flatulence (gas) pass through the anal canal and hits your buttocks which cause the sound. Depending on how a personage is sitting,standing, lying, etc. the exit of the flatulence will make a different clamour. Also, pressure will affect the noise, or shortage there of, too.
I am sure that near is a scientific point for this. I would just deduce it is the amount of pressure behind the gas. If you push it, it have alot of pressure, and it will be louder. If you are relaxed they kind of slide right out silent resembling.
It probably has to do next to two things. The speed and or force the gas is leaving your body combined beside resistance you put into it. IE if you are sitting down then it doesn't own an easy exit ... you grasp the point. LOL.
Velocity.
my friend was babysitting soon, and was concerned around the baby have green feces, so she called me and asked me to look up the cause (because i was close to a computer and she wasn't)... i googled "green poop" and came up near a funny but informative site... i think it be "smellypoop.com".
this sounds a little rediculous, and parts of the site are a bit much, but it does own good information! i would suggest reading it and relaying the info to your son... hope this help!