I tried something similiar several years ago with a Shih Tzu. We didn't have any success with it. She never got the connection between barking and the noise, I don't think. (But then, she definitely was one of the dimmest "bulbs in the box"). She'd bark, hear the noise, look around, and immediately go back to barking.
You might do some reading about separation anxiety in dogs as I'd guess there is a good chance that's why Bella is barking. You might also look into the DAP diffuser which is supposed to be calming. Here is a good article on separation anxiety:
http://www.clickersolutions.com/articles/2002/sa.htm
Good luck!