I have a Whirlpool microwave model #WMH53520AS. Even since they installed it, it's very loud. I thought something was wrong with the exhaust, which had been there previously. I climbed up and looked at the top of the microwave -- over the door that opens of the microwave -- the cap that says Whirlpool. and I see that there's nothing covering that part. Should there be some kind of cover on the top of that cap??