Why do farts vary the way they do?

How come when I break wind, sometimes I hear nothing, yet other times the sound is loud enough to scare my cat in another room (not to mention the spasms she gets when the smell reaches her…)? Why is it that even though I think I emit the gas excactly the same way, the results are so unpredictable?
What makes the sound of a fart? I think it’s the sphincter vibrating in the process, but how come it doesn’t vibrate the same way even with two consecutive blasts just seconds apart?
Why do SBD’s smell so much worse than loud farts? If diet is the leading factor behind the lethality of a fart, does it also regulate the sphincter? How is that possible? Has anyone really delved deep into the dynamics and theory of flatulence?

Different smokes for different folks.

The sound is due to your ass cheeks flapping apart and back together. I’ve noticed no corellation between noise and smell whatsoever.

Never heard of the terrifying, “Silent but deadly”?

My elder bro only eats fruit and veg and he’s convinced his farts don’t smell anymore. (He recently moved back home and I have to say it’s been pretty fart-smell-free… but my lil’ bro’s taken it upon himself to work hard to make up for the lack of said smell)

Even if my elder bro doesn’t stink the place down, dear GOD can he let rip! The picture’s on the wall tremble! … but no smell, so it’s not all bad.