Apple Final Cut Pro 7 - Manual (Page 686)

2 Create a new sequence, name it “Room Tone,” and paste the audio pause into it twice.
Paste the pause section
you just copied twice
into a new sequence.
3 Select the clip containing the second pause, then choose Modify > Speed.
4 In the Speed dialog, click the Reverse checkbox to select it.
5 Play the resulting clips.
The looping sound should be gone, but if you hear a clicking at the edit point between
the two clips, you may have to add a cross fade transition between them to smooth this
out. For more information, see
“Adding Transitions.”
If the looping effect is not obvious, you may want to skip the speed reversal step. You
may also need a longer section of ambient tone, or several different sections. Experiment
to see what works best.
6 Cut and paste as many pairs of these clips as you need to fill the necessary duration,
adding cross fades between each pair.
686 Chapter 43 Audio Editing Basics