Clean as a Whistle

Where does this phrase come from?

The obvious one is that a clean whistle produces the clearest tone. Any damage, debris or moisture could affect that. It is usually used to describe someone as blameless, guiltless and so on.

A more intriguing possible meaning is that of a simile describing the sound made by a sharp sword as it whistles through the air on the way down to cleanly decapitate a victim!

Either way, here is an actual whistle, shined up clean for the WBC theme of 'CLEAN' this week.