Does your site talk to anyone?
This is a question I recently had when I was dealing with a really slow dashboard. I knew WordPress tried to load news from WordPress.org and even planet.WordPress.org. I knew there could be other situations where it loads data from somewhere else after all it shows new themes and plugins.
I was trying to figure how I could find all the URLs so I could get them white-listed for this particular site. Then I realised that I could not find it in the code itself because many of the URLs would likely be dynamic. I was trying to figure out what my next step would be. Then I had a thought, I would just build a plugin and hook into pre_http_request to find all the URLs it attempted to communicate with.
This was a really simple plugin and after running it for a few days the findings were very interested, especially with a few common plugins installed.
You can download Remote Requests here.