I have a 2004 Pontiac Montana, and it just started making a low buzzing vibration noise when it’s in motion. tone/pitch only changes with vehicle speed, not engine RPM. It becomes noticeable at about 20 MPH. Pitch starts low, gets a bit higher and faster as speed increases. Have looked for anything loose, nothing found. Braking is not a factor in the sound. Tires are good, Engine doesn’t seem to be tied to the noise. Nothing noticed on body panels, air dam, etc… I suspect either transmission or possibly U-Joints.
Thoughts?
Dry U-joints needing a lube could cause this possibly. Pretty much anything in the drive chain, from the crankshaft output, to the wheels, brakes included. Axel bearings on the fritz can make this kind of noise too, but usually it is more of a growl than a buzz. Brake noise usually occurs at first only when applying the brakes, so I’d discount that unless proved otherwise. If yours was a front wheel drive, I’d first have suspected CV joints needing a new boot and and rebuild. Maybe start with your mechanic inspecting the driveline and rear diff.
You have a transverse mounted engine, so it’s most likely FWD, perhaps AWD
If it’s front wheel drive, you DON’T have a driveshaft and u-joints
I suspect you have bad front wheel bearings. If a shop confirms this, have them replace both.
Example: if the left front bearing is bad, have them replace left front AND right front
Have you looked for the missing flexible baffle that should be across the top of the engine just in front of the windshield when the hood is up? Should block air flow up under the hood. This thing sits on a raised metal lip. Gets left off by careless mechanics. Also, how much of your bumper dam is missing or cracked from driving into parking lot barriers and curbs. My 2003 has lost most of this useless item over the years, and the remaining parts tend to whistle through the cracks and across the jagged edges.