Once the car reaches about 80 miles per hour, a buzzing/humming noise is emitted from the front of the car. I can’t tell whether it’s from the dashboard area or the footwell area, but it sounds like it’s coming from below. There seems to be an exact speed where the noise stops and ends. The car does not shake or vibrate when the noise occurs.
The noise has happened twice. Not coincidentally, those were the only two time the car has been above 75 or so miles per hour within the past few weeks.
I have looked on some forums for similar happenings, and I found the answer could be bad wheel bearings.
If it helps to pinpoint the problem, other problems with the car include a very-vibraty engine between 1000 & 1500 RPM, a gurgling noise at low speeds/idle, and harsh shifting from 2nd to 3rd gear.
I’ve posted a video on YouTube of the car making the noise. It’s a little hard to hear the noise in the video, but I hope it helps.
Have you ever had the windshield replaced in the vehicle? I once rented a Ford Taurus and there was a terrible buzzing noise when the car reached 50 mph. I returned it to the rental agency and we got a free upgrade to a Jeep Grand Cherokee. The agent explained that the Taurus had just had the windshield replaced and it wasn’t sealed correctly.
Here’s some ideas anyway. Make sure all the windows are completely rolled up. Check each, one by one. Sometimes a noise like that can occur if a window is down 1/16 inch, not visibly down, but enough to allow some air flow. Like your symptom, when this occurs, the noise is affected by speed. Often it will make a noise at one speed, but not another. Or make different noises at different speeds. The passenger compartment becomes a baffle in resonant sound chamber I guess is why it happens.
Other things to consider are indeed the wheel bearings, and something loose under the car, like the engine windscreen or the cat heat shield. You local inde mechanic can easily confirm if either of these are the problem.
I had a similar problem once in a Toyota Tacoma and found that the top edge of the dashboard was vibrating against the windshield at certain speeds. I wedged a piece of cardboard in there and the buzzing stopped.
One highway, actually. The SH-130/SH-45 bypass around Round Rock and Austin has an 80 MPH limit. The total is about 54 miles at 80.
I’ve owned cars with buzzing from the dashboard. Push on different parts of the dash with your hand to see if it stops. Once you isolate it,you might be able to fix it. A friend with an early 1970s Camaro fixed his by applying an adhesive to every spot he isolated with a buzz.
Wheel bearing make noise at all speeds, its kind of a roaring sound, like snow tires on a clear road. The noise gets louder when turning in one direction, quieter when turning in the other.
@db4960, I just looked it up on the Texas DMV web site. I read a few months ago that Texas was increasing the speed limit on one road to 80. They’d do have several roads where the limit is 75 though. In Maryland, interstate max speeds are 65 near large metro areas and 70 in other areas. That’s fast enough for me,and for much of the day you can’t get anywhere close to the speed limit because of dense traffic.
My experience with bad front wheel bearings on a FWD sedan matches @Keith 's above, a roaring sound when going straight ahead, or using snow tires on a dry road, sounds like the road surface is rough rather than smooth, and the roar gets louder the faster you go. Most noticeable above 50 mph. Really noticeable at 70 mph.
On the rear wheels of a FWD sedan, which just coast along, the sound for me was more noticeable when turning 90 degree corners (like in neighborhoods) at slower speeds than when going faster but straight. For the rear wheels, the sound when turning at slower speeds isn’t so much as a “roar” but a sort of a modulated sound that varies in intensity over a couple seconds interval , like comes from an automatic dishwasher on the wash cycle … a rrrrr — rrrrrr —rrrrrr sound.