Split stereo to mono to remove swear words but it ruined sound quality

Hello, Im brand new to this software and was looking for a little help. I’m trying to help a buddy of mine who’s a local music manager to create a radio edit of one of his artists songs. I’m following a tutorial on how to do this with audacity, it has me split the stereo track to mono and invert the selected lyrics to be censored on the top mono track. This works great but spliting the track to mono seems to ruin the sound quality, making it sound noisy and crackly. On the videos i watched they didnt have that problem, what am i doing wrong?

Instead of splitting the track, try using the “Vocal Remover” effect just on the word that you want to remove: