I have tried and tried to figure out what this is and I cannot. Hopefully someone on here will be able to help me. I have a 2007 Base model Grand Prix with 58,xxx on the clock. When I am driving on the highway I get a loud howling noise (like when I run over the lines on the road that are supposed to wake you up as if you are about to run off the road or if you are blowing air across the top of a coke bottle) that sounds like it is coming from the firewall of the car. It starts around 60 mph and grows louder/more constant when I accelerate to 80 mph. I've not had the car more than 80 yet. It does it when I have the windows and the sunroof all closed/rolled up but when I click the sunroof to open it stops. It's not the AC vents being sort of closed. Any suggestions would be great! Here are some of the things I've been told it could be:
Tires cupping
Transmission Mount
Windshield
Wheel Bearings
Blower Motor for AC (which I don't think it is because it does not stop when I turn the AC off)
Power Steering Pump (this made a similar noise but when I put fluid in the pump it stopped--this was more of a whine versus a howling)
Again, any suggestions would be great!
*****UPDATE*****
I drove on the highway on the way to get the car washed to test the windshield and sunroof for leaks...the noise would start now about 70-75mph and would stop when either of the two front windows were cracked. It would NOT stop when the rear windows were rolled down. The window and sunroof did not leak when I went through the auto car wash. I am still going to check the seals but since I found out my front tire...not the rear like the TPS said it was was low on air, I am going to take it down the highway again and see if it was just the tires howling...will post another update when I can. Thanks for all the suggestions.
*****UPDATE*****
It was NOT the tire that was low...I ran it up to 90 mph today and at first it didn't make the noise...then on the way back from town it howled like a banshee...it also DID NOT change volume when changing lanes...will try looking at the seals around the window and sunroof later...I was also told to check the heater to see if there is a vacuum leak...
