Those notifications are usually generated by the individual posting the file. When an individual chooses to post a file to the groups, there is a little check box in the bottom left corner that says: "Send a message to the group announcing this file."
This allows the posting individual to tell the world he/she has posted something useful, or, possibly, something just simply annoying! There is no setting in your preferences that I am aware of that stops this type of message. Louis - K5STX
