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

I'd be happier to help if you didn't have the little "mad face" up, makes me think you are mad at those you want to help, although I know you are mad at the truck.
The fan cage is likely plugged with leaves or other organic material. It's easy to lower the passenger side under dash panel, remove about 4 screws, pull out the blower and inspect/clean it. If you are DIY inclined at all, here's your chance! Could also be the dust filter plugged, you can access that easy from the same area.
There is a "fix" for the blower fan plugging up, involves some foam plugs to block some areas of the cowl intake to keep stuff from getting sucked/falling in there.
Gilly

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Thank you for the reply, Gilly.
I wasn't angry...... my silly wife was fooling around with the smilies.
I'll do as you suggested. So, I gather from your answer that there is no fan or motor under the center of the dash near the windshield. If so, it is probably referred sound from a plugged up duct. I changed the in cabin filter myself so I guess it is in that area.
Again, thank you for your help.

I'm pretty sure you'll find a bunch of stuff in the blower fan, seen lot's of types of stuff, usually "natural" things like leaves, acorns, or other "tree" stuff, but I've also seen critters bring things into the area too, such as dog food or chewed up insulation to use as bedding/nesting. Sounds like what you described, usually with an out-of-balance buzzing/vibrating noise.
This is the only blower fan for the climate system.
Gilly

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Well, Gilly.... you were right. I took the fan cage down and there were a few dead leaves in it.. enough to make a clogging sound. I put my hand up through the duct and it was clear on top. There were three hex screws to take off. Fan sounds beautiful and quiet.... like new now.
Thanks again.
Dr. 007