Apple Final Cut Pro 5 - Manual (Page 918)

Chapter 7 Mixing Audio in the Timeline and Viewer 131
I
The two inner keyframes surround the problem samples, while the two outer
keyframes are placed a few hundredths of a frame outside of these.
6 Drag the part of the level overlay between the two inner keyframes down until the box
indicates –60 dB.
The unwanted noise should be gone, and the rest of your clip’s audio is not affected.
The problem samples
The overlay looks
something like this.