"Rustle" is the sound of leaves moving against each other. "A rustle of trees" is a literal phrase, as well as "a rustle of paper" (a sheet of paper in a book is called a leaf). You understand what that sounds like. People whispering can sound like leaves rustling in trees, so you can use "a rustle of whispers" figuratively. "To rustle up a meal" is figurative. It probably comes from hunting game birds for food, as someone would need to shake the trees and bushes (=leaves rustling) to scare the birds out of hiding. In the idiomatic sense, it means you don't know what to cook and you don't have a plan, but you'll go and see what you have, and try to make something out of that. If you're anything above intermediate level in English, you should know this word.

Yes - I would rustle up a meal. Leaves are rustling in the trees outside. My cat loves to rustle through the papers on my desk. No - I might hear a murmur of whispers, but not a rustle.