Why do farts smell bad?
Fart odor due to hydrogen sulfide & mercaptan content. Both of these compounds contain sulfur (sulfur). The more sulfur content in your diet, the more sulphides & mercaptans produced by bacteria in the stomach, & the more foul you fart. Eggs & meat have a big role in producing fart smell. Nuts play a role in producing volume of farts, not in rottenness.
Why does a fart cause a sound?
Because of the vibration of the anal canal when the fart is produced. The sound of sound depends on the speed of the gas.
Why is that foul fart that's warm & noiseless?
One source of fart is bacteria. Bacterial fermentation & digestion process produce heat, the byproducts are rotten gas. The size of a gas bubble is smaller, warmer & saturated with a rotten product of bacterial metabolism. This then becomes fart, although only small volume, but SBD (Silent But Deadly).