I downloaded the nyquist noise gate plug in and installed it per the instructions. Moved the file to the Applications-->Audactity-->Plugins folder.
I can see the file (9kb) there.
I have restarted Audacity but do not see it in my Effects. If I go to the add/remove effects, I also do not see it in there.
More odd behavior...after I placed the file in the plugin folder, it seems like many of my effect options have disappeared. I use only a few, so I do not know which ones, but there used to be (I believ) Nyquist plugins at the bottom of that list that are no longer there.
In the add remove effects box, there is one for NYQUIST and when I enable that it never seems to take.