What is this horrible noise in our new Class C?

Great thoughts! Thank you. I don't think it's the vents. We hear the noise when they are closed and we do have brand new vent covers installed. I will have to check the stove vent flap. Where is it located? Would it result in a sound that is coming from just above the windshield where the cab meets the bottom of the top bunk (i.e.: just over the visors)? I'm told Miine Winnie are typically pretty solid so I hope it's something simple. Thanks again for your help.