Controlling 2 audio loops

I’m making a Flash presentation for a window company, and what they want is an animation of a customer’s original window that can go up and down (which is easy enough) but the audio loop in the background to go from normal volume, down to maybe 10% when closed (and of course up to 100% again when opened), to show that your original window won’t block all sounds out.
But there will also be a second inner window (their product) which will be 0% volume when closed.

These windows need to be able to open and close alternately, and together, and I’m just having a bit of trouble getting the original window to fade out to 10%, when the new window is open, and not make any noise when the new window is closed.

Hopefully this isn’t all that confusing, and that some kind soul will be able to send their audio expertise my way.

Happy new year, and all that hoohar. Thanx in advance.