Go into Adobe Audition and cut the wavelength shorter.
Flash can repeat and fade sound, but it can't cut the duration of a wavelength. There is one other option I can think of right in Flash, and that is to cut off the volume of the audio to cut its duration. However, the clip will still load in its entirety and and should cause more data load than necessary. The best would be to cut the wavelength of the clip itself through Audition or another audio editor.
Keep in mind though that I haven't used the newest Flash versions, so they may have improved the audio editing engine since then, possibly including a wavelength editor. They've done that with Premiere and the rest, after all.