See Noise Removal for tips on removing clicks and pops from vinyl recordings.
Repairing Popping Vocals
Here's how to repair popping or percussive vocals. It'll never be as perfect as a good original recording.
1. Make sure the recording's DC offset is zeroed. (This in itself will eliminate one possible cause of clicks generated by subsequent edits and silences and should be done before you do any editing). Do this by selecting the whole track and choosing the 'Normalize' effect. In the resulting box make sure you've only selected "Remove DC offset".
2. Zoom in on the percussive sound. They're easy to pick up. They look like a big single waveform just before the rest of the sound.
3. Select this waveform and then choose the 'fade in' effect. This will soften the percussive and hopefully solve your problem.
4. Since these percussive sounds are mostly very low in frequency, some users have reported great success using the 'high pass' effect instead of the 'fade in' effect as suggested in step #3, above. Note that the 'high pass' effect can be repeated multiple times on the same selection. This approach has an additional advantage of not interfering with or reducing the level of higher frequency sounds, an advantage when the vocal percussive sound was recorded along with other instruments or sounds.