Possibly stupid question

I’m trying to add sound to some buttons. It’s just a little metallic ‘klink’ sound that plays on rollover.

I only want the sound to play on the ‘Over’ state. So I’ve set up a layer (just for sound) for the button and I add my sound in the 2nd frame (the Over state).

Everything is cool. All is good. And the sound plays on rollover.

But the sound also plays when I click the button (i.e. it also plays on the “Down” state). Why? The Down state keyframe is completely empty.

What’s going on here? I’ve only put the sound in the “Over” keyframe, why does it also play in the “Down” frame (or when I click)?

Thanks.