There is something inserting the two words social network in my title tags. Where is the coming from?
Social Network
Hmmm. Most likely it's from admin/core/settings/general "Site Title"
If you view source here, you can see the "SE Community" follows the general page title.
<title>Title Tag Demon - SE Community</title>
Check there first. If not that, you could have a third party plugin that maybe offers some SEO settings.