Comment 1 for bug 1495047

I assume you "buffer indicator" the the "Audio Latency Usage Meter".
By the selected Audio Buffer in hardware preferences, you define the 100 % lets say 23 ms.
For a non crackling sound, Mixxx has to process chunks of 23 ms samples in time < 23 ms.
If it takes 11 ms the "Audio Latency Usage Meter" is at 50 %. If it takes 24 ms, one chunk is skipped.

I guess you use a non SSE build. I had exactly the same issues on Linux.

You should use at least
scons optimize=portable
or just
scons

Even if a Deck is paused the silence stream is processed. If the samples are not exactly 0 but near, the CPU uses a lot of extra cycles to still produce scientific exact results.
https://en.wikipedia.org/wiki/Denormal_number

We have to bes sure that the de-normals are treated as 0, to prevent this issue on Windows as well.
This should happen here
https://github.com/mixxxdj/mixxx/blob/3f854c1674084609497036ba92e1605a43fb492f/src/sounddeviceportaudio.cpp#L772

do you see the
"SSE: Enabling denormals to zero mode"
log message?