Interesting question. I don't know if this will work or not. It works for
entire sounds, so try it and let us know.
1. Mark the selection with the start and finish markers, which are left and
right brackets.
2. Play the selection so you are with in that marked area.
3. Go to effects, noise reduction, and select a setting.
4. Use preview to hear the results.
5. Apply the chosen setting.
Let us know.