You may or may not want invoice creation appearing in the chatter feed. You can control these settings in Salesforce Setup.
You can find this setting in Setup > Customize > Chatter > Feed Tracking (or search setup for 'Feed Tracking'). Find the Invoice object in the list of Objects.
From here, you can enable, or disable, Chatter Feed Tracking for the Invoice.
However, this is only one of the settings that can cause Invoice activity to affect Chatter. If you are still getting Chatter activity on Invoices, you may wish to go to Setup > Customize > Chatter > Feed Tracking (the same screen as above) and then go to the User. Uncheck "All Related Objects". Please be aware this may have company wide implications, and other related objects might stop posting updates to Chatter.