Ricky can laugh it up about the UFO magazine and the horse in the pub, but Karl is correct that there are only so many noises that can occur.
The piano keyboard analogy is actually kind of brilliant.
Where Karl gets it wrong is his estimate that all noises have been used five times. More likely there are many that have never been heard and never will be heard. But that doesn’t mean that sounds can’t recur — some things do sound very similar to other things.
Some birds imitate other birds. Humans imitate each other — and other sounds. And then there’s recording and digital reproduction of sounds. In point of fact, we do end up hearing a lot of the same stuff over and over and over. It’s probably not all that common that you hear a completely novel sound.