I’ve spent 3 entire days trying to clean up my audio, but I can’t figure out a few things. After using Noise Removal, Audacity did remove all the static from the song, but it replaced all the static with what sounds like a slow leak in a car tire. LOL How do I remove this and replace it with all silence? The other problem is there’s a pop in one part – and I’ve tried so many things to remove it – including Repair, checking the waveform and making sure there’s no irregular pattern, using the Pencil and manually redrawing any part of the waveform I thought looked broken in the area I thought the pop was, Cross Fade, and Zero Crossings – but the pop is still there. 
Please explain how I can fix these things so I can export the audio. Thank you.
You are the next vote to stop calling it Noise Removal and start calling Noise Reduction. Noise Removal tries to carefully build sharp filters to remove the offending sound without affecting the show. The best you can do is mostly reduce most of the noise without damaging too much of the show. Try running Noise Removal again and be Very Careful to do the Profile step in a place that has only bad sound and no show. That’s very important. Then use light reduction values (first number). Don’t go straight for the dead quiet studio recording. Most shows never get there.
We can’t do anything about echoes or other performances mixed in by accident, like dogs barking or the TV next door.
If you have enough of a serious pop in the show, then there is no show back there to rescue. You can reduce the pop to nothing, but all the show in that portion of the waves will go, too.
Magnify the pop until it’s most of the screen.
http://manual.audacityteam.org/o/man/zooming.html
Drag-select the waves that make the pop (keep dragging, playing and selecting until you get the whole thing). Reduce them to flat line with Control-L. You can also cut them out of the show with the DEL key and try to match up the two raw ends with the editing keys.
Koz
I forgot to mention that I also tried deleting the pop, but unless I delete a huge chunk of the audio, it’s always back.
What is the pop? Somebody open a can of cream soda in the middle of the performance? Gas main go up?
Unless you can “borrow” notes from another part of the performance (same phrase from somewhere else) you should start scheduling a reshoot. And while you’re reshooting, try and find the other noises and get rid of them before you press Record. Hiss is a real problem. That’s very difficult to get rid of in post production.
Koz
Nah, I’m not rerecording. I’ll try a little more editing, but if no success, I’ll just cancel the defects out with the music track.