mic loop on Audacity

New Audacity user here. I’m on Audacity 2.0.5, Mac Book OS X 9.2.
Some how I’ve enabled some mic setting in Audacity that is sending out a crazy feedback loop (high pitched warble) whenever I open a New File and click on the little mic setting to monitor my input and output.
I can hear my voice echo back at me, in addition to the crazy loop.
Any suggestions on how I get out of this, please?
thanking you.
Carl in Tucson

Try unchecking “software playthrough” in Audacity preferences
Audacity Preferences, Recording, Software playthrough is unchecked (coloured yellow here).gif