When you say "hey, that's a cool sound" and then get together with your friends, you're not going to create a perfect copy of that sound, no matter how hard you try. First off, you didn't hear that sound in the exact same way it was produced--you heard it through the distortions caused by the radio and the structure of your ears and skull. And when you perform it, the tune will be changed by your imperfect memories, your skill level, your particular instruments, your ability to keep rhythm, the acoustics of your current location, and the agility and strength behind your hands and breath (depending on what instrument you play). Even if you get the sheet music and the original, it will still be at least a little different from the original. But most likely, you're going to be putting your own spin on this piece, even if only unconsciously, unless you make an effort to copy the music as exactly as possible. And even then, it will still be a little bit different.