If you are still having audio problems on Windows 7 or Windows Vista, please follow the following steps and see if it fixes the issue:
1. Go to Start > Control Panel.
2. Double-click on the Sound icon.
3. Single-click the Speakers to highlight them.
4. Click on Properties near the bottom right corner.
5. Go to the Enhancements tab and click on it. If you don't have an Enhacements tab, you may have a tab called "SoundBlaster".
6. Make sure "Disable all sound effects" is checked. Or if you have a "SoundBlaster" tab, make sure the checkbox labeled "Disable enhancements" is checked.
7. Click OK
8. Play Defense Grid!
I'd very much appreciate users that are having audio problems reply to this thread saying if the above steps did or did not fix their problem.
I would also like to thank the users that worked with me through email to help come up with this solution. Hopefully this solution will work for anyone else still having problems!