I wrote up what I've found good (and some not so good) about the Volt after 3 weeks of owning and driving it. The full write-up is over on Google+ but feel free to ask questions or tell me anything I got wrong either here or there.
Most of the areas for improvement I can't help you with but they do make an alternative air dam for the front which is much shorter and as such won't scrape when going over speed bumps. This should be available through the dealer. Removing it entirely is also easily done. Either will affect your mileage somewhat but may be worth it should the sound continue to irritate you.