Apple Final Cut Pro 7 - Manual (Page 939)

The two inner keyframes surround the problem samples, and the two outer keyframes
are placed a few hundredths of a frame outside of these.
The problem samples
6 Drag the part of the audio level overlay between the two inner keyframes down until the
box indicates –60 dB.
The overlay looks
something like this.
The unwanted noise should be gone, and the rest of your clip’s audio is not affected.
Example: Using Keyframes to Control Pan
Setting keyframes to change pan dynamically works the same way as setting keyframes
to change levels dynamically. You need to set at least two keyframes to effect a change
over time.
939 Chapter 57 Mixing Audio in the Timeline and Viewer