Dell has some good hardware forums at their site you can use if your warranty has expired. I'm not sure what you mean by empty drive bay. If there's truly nothing in the bay, you could use glue to keep it closed. I wouldn't use super glue if you think you'd ever want to install something in that bay though.
The door for the blank CD/DVD drive bay on the front of my XPS-9000 keeps opening. I keep closing it. Any ideas on how to keep it closed?