Site Audit will flag any pages found to have the Noindex directive under the "Noindex page" issue.
When should I use "noindex" meta tag?
You should only use this tag on the pages you don't want to appear in search results.
If you want a page to be indexed by search engines, you should remove this tag.
Be sure to also check Google's guidelines on the implementation of this tag here - https://support.google.com/webmasters/answer/93710?hl=en