Truck is a 99'430 ML. With fan speed on medium and high, the fan sound from under the windshield sounds like a clogged vaccuum cleaner. When I turn the temp control down it is less but when turned up, for heat, the sound intensifies. The fan seems to go faster. (I have a new cabin fan filter, the one under the glove box.) Is there a fan motor under the windshield grill that could be going bad? or a duct or vent that I could get at easily to check?

rsl007