“What's that rustling noise?”
You're camping with some friends. You're worried about dangerous animals. You hear a noise when you're laying in your tent, so you ask your friends about it.
What's that rustling noise?
Ask this question when you hear a noise that you don't recognize. You want to know what caused the noise.
You can ask this:
What's that noise?
Or you can ask about a specific type of noise:
What's that howling?
What's that creaking?
A "rustling" noise is the kind of noise that's caused when leaves rub against each other. An animal walking through the forest might make a "rustling" sound, for example. You can also hear "rustling" when you move pieces of paper around and they rub against each other.