The only thing that is checked all the time is:
1. Code Assistant
When you are editing and type . , or ( the database is accessed to obtain a description of the object. You can go to Tools > Preferences > Code Assistant and disable the "Automatically activated" preference. Now you have to explicitly press F6 to invoke it.
2. Check connection
If this preference (Tools > Preferences > Options tab page) is activated, the connection will be checked once a minute. You can disable this option.
3. Transaction check
Whenever a new Window is brought to front, the transaction state of the session of that window is checked to update the Commit and Rollback buttons. This is improved in 6.0.
If you notice any other activity besides this, let me know.