it is your fans man the vibation of them is making the sound .................the only way to fix it is to change the fan ..............u want to get computer fans they are designed to be quite it is way u see so many of them in boxes
i am assuming those fans are 4 or 6 inchs ..............
here is a 200mm (8 inch) computer fan .........u can inlarge the hole little and use this the noise will almost be gone
here is how to do it u can use a 12 volt plug from anything that u have that u do not want or no longer works correctly
[video=youtube;N9DMTQ2e7oM]http://www.youtube.com/watch?v=N9DMTQ2e7oM[/video]
hit walmart too and grab this ....................... u take th probe and put it in side and hang half way so u can look and see what it is in there with out opening
u have not accounted for smell blocking .................when u are ready for this info tell me i have a method to help controll it( i have confirmed it worked with mine)