This is specific to Mac, and is the most common cause of glitching on modern Macs. On other platforms (Windows / Linux), the usual approach would be to increase the buffer length, but Apple did something a few years ago to the Mac sound system and we suddenly found that a lot of Mac users started getting clicks in their recordings. After some experimentation, we found that Audacity’s default 100 ms buffer size was implicated (although that has been the default for over a decade). The solution to this specific problem was to decrease Audacity’s buffer size. As far as I’m aware, Apple has never released information about the change that caused this, but if anyone knows otherwise, we would love to hear.
While less common on Mac computers, there’s a host of other things that can cause audio glitches. This page in the manual covers many of them: FAQ:Recording - Troubleshooting - Audacity Manual and more on the wiki: Missing features - Audacity Support . Although that article is written mostly from a Windows perspective, many of the issues can also apply to Mac and Linux