MC20 worked perfectly.
In order to download the new MC21, it required me to delete the older MC20.
Hmm, not sure what you mean there. I have MC20 and MC21 installed in my Applications folder. They are separate and I can use either one of them. Have you dragged MC21 into the Applications folder? That's the normal way to install most Apps/Programs on Mac. (Not trying to be patronizing; some people don't know how to install Mac apps.)
Once it downloaded, I just re-selected my music files and downloaded them.
I also had to reinstall all my original settings - Not a big deal.
I just cannot understand why the audio keeps cutting in and out now?
I'm guessing some of your audio settings are different. A BIG one that's caused a good number of people problems is the Hardware Buffering setting. Please go check yours at:
Tools > Options > Audio > Device Settings > Buffering > Hardware
If it's set to "maximum", set it to Hardware Default instead. Then stop and restart MC21 and try it again.
Good luck!
Brian.