You can combine sine waves in an infinite number of ways, so I think it's safe to assume there are plenty of sounds nobody has ever heard before. To some degre

You can combine sine waves in an infinite number of ways, so I think it's safe to assume there are plenty of sounds nobody has ever heard before. To some degree, it's about how you group things. If you believe a guitar and a banjo are similar enough to qualify as the "same" sound – then no, there's probably not too much left to discover. But if small subtleties in timbre are fair game, then there's basically a limitless supply of new sounds.