How do get rid of rattling sound in brand new bathroom exhaust fan?

I just installed a brand new Broan bathroom exhaust fan and it makes a loud rattling sound. I took down the unit and when I turn it to its side or upside down, the rattling goes away. It only makes the sound when in the normal operating position. I tried adjusting some screws that are attached to the motor, but was not successful. Is this a defect and should I just return it?

Thanks
This is a $70 model with a scones rating of 2.5.

Answer
open up the cover, find the rattle, wedge it with something