Honestly that "ear for an engine" thing is so true, it really is a lost skill. The computers just give a code now, you don't need to listen to anything. Sager17 is right, it's a real shame.
My dad was a mechanic and he'd have me listen for a specific hum or a slight tick when things were warming up. You could tell a lifter was getting tired or a belt was going bad just by the pitch. Now it's all OBD readers and guessing, which just isn't the same.