Belts flapping when AC is on?

Thanks guys. The compressor used to be a bit annoying at idle and low speeds and relatively smooth at freeway speeds. Now it's getting pretty bad to the point where I don't even use it anymore for fear of something going wrong. Doesn't sound right at freeway speeds anymore either.

How do I even go about getting a matched set?

Also would low oil in the compressor have anything to do with it?