We all like cars with powerful engines. But we also prefer engines that are relatively quiet, so that you can enjoy a peaceful ride. A humming noise that gets steadily louder as you increase your driving speed is a huge pain, and can also be quite concerning.
The humming noise itself is not an issue, but it could be a signifier that something else is awry with your vehicle. There’s no need to panic, and this is not one of those cases where we recommend an immediate halt on the driving. However, it’s definitely worth looking into the cause for the humming noise and trying to solve the problem before it rears its head in another malfunctioning car part.
So why does my car making humming noise at 40 mph?
Here are a couple of reasons why your car makes a humming noise when you speed up to 40mph:
- Wheel and tire issues
- Loose wheel bearings
- Drive shaft
- Vacuum Hose Leak
Read on to find out how to troubleshoot, identify and solve all the possible issues associated with your car making a humming noise, especially at 40mph.
However, if you think the sound your car is making is less of humming noise and more of gurgling noise, that’s a separate issue and you should probably check out our article here.
Top 4 Reasons Why Your Car Making Humming Noise at 40 mph
Here are the most common and plausible reasons why you’re experiencing the strange humming noise. Identifying the issue early on can go a long way in taking care of your vehicle and extending the life of various parts.
Reason #1: Wheel and Tire Issues
The reason why we’ve listed this reason as the first one is because it is the most common explanation for a humming noise. There are a couple of things that can go wrong with your wheels.
An imbalance in the wheels is an issue that mechanics see all the time. An imbalance can occur very easily, and this causes too much weight to be shifted to one side of the vehicle, for one wheel to handle. The uneven weight distribution is a major culprit for why you experience the strange vibration and noise.
Speaking of uneven, it’s also common to have this kind of sound produced when one of your tires is older than the other. If you’re driving with a very old tire and a brand new one, the old tire will have signs of wear and tear that the new one won’t. This will also result in an uneven driving experience that can lead to wrong weight distribution and noise.
Your wheels need to be identical to each other. If one wheel is too far away from the center of the axis, this can lead to a phenomenon called radial runout. Radial runout means that the wheel is actually spinning in a circle that’s different from the others, and this can seriously damage the wheel parts as well as cause a whining and humming noise. Radial runout is particularly heard as you speed up to 40mph and beyond, which perfectly explains the issue.
Similarly, lateral runout is another issue that drivers can run into: however, it’s much more common that lateral runout causes a louder humming noise only past 60mph. Still, it is not impossible that you’re hearing the noise at 40mph and is definitely something you should check out.
Furthermore, any additional damage to the wheel parts, such as the inner belt and strands can also cause movement which can lead to the humming noise.
Solution: Checking the tires should be your first task on priority once you’re identifying a humming noise at 40mph. Most of the time, the cause for the issue will be something to do with the tires. Make sure that they are in alignment and also that there’s no uneven distribution of weight, or uneven wear and tear. You can do this part on your own and try to find out what the issue is.
However, if it seems like there is no unevenness in the wear and tear and alignment, get your tires checked for both radial runout and lateral runout by a professional. This might be the reason for the issue.
No matter what the issue is with your tires, they are usually fixed easily and don’t require a replacement (unless one tire is very old and has significant wear and tear).
Reason #2: Loose Wheel Bearings
Your wheel bearings should always be in good condition. If your wheel bearings have gotten rusted, or just dry after years of use: they might get loose and stop working perfectly. This can also cause a lot of humming and other disturbing noises.
Solution: Take a good look at the wheel bearings. They might be too loose for the vehicle, and it will definitely help to tighten them. However, if you note that they’re dry or worn out, you might want to source replacement wheel bearings.
Reason #3: Drive Shaft
If your car has rear-wheel drive then you might want to take a closer look at the driveshaft. A driveshaft that is in perfect working order will be balanced and aligned straight and is supposed to match engine speeds at high speeds — but if there’s an issue due to wear and tear or imbalance, this can cause the humming noise.
The drive shaft ordinarily assists the transfer of rotating power directly from the transmission, so you can see why any issues with the drive shaft can impact the car negatively.
Solution: Take a look at the driveshaft. It should be balanced properly and shouldn’t have any rust or corrosion on it. If the driveshaft is indeed imbalanced, then it’s easy enough to straighten it and fix the issue entirely on your own without having to call a professional.
Reason #4: Vacuum Hose Leak
It’s very plausible that the vibrational noise is coming from the engine instead of the other parts of the vehicle. You can face this issue at higher speeds like 40 mph if there is some issue with the vacuum hose.
The vacuum hose is responsible for maintaining the appropriate air to fuel ratio. If there’s any leak or tear in the vacuum hose itself, this can seriously compromise the air-to-fuel ratio, and negatively affect the engine’s performance. If left for a long period of time, this can even cause the cylinders to misfire, internal damage to the engine and even a drop in fuel efficiency. That’s why it’s so important to take a good look at the vacuum hose.
In addition to experiencing vibrations at the 30mph, you’ll also typically witness a similar vibration when you leave your car on idle. For those of you who don’t know, leaving your car on idle refers to leaving the engine on when you’re stationary. This can be a great way to double check if the vacuum hose is really at fault, since vibration at idling is a good confirmation of the issue.
Solution: If your vacuum hose has a leak, there’s no way around it — you will have to repair it. However, we suggest replacing the vacuum hose instead of trying to repair the leak. Repairing a leak doesn’t last long and you’ll often find more leaks in the same vacuum hose.
While there’s no need to panic, it’s a good idea to ensure that you deal with the humming noise as soon as possible. It could be a small problem like uneven weight distribution with the wheels, loose bearings, or something far more serious like a vacuum hose leak. Whatever the reason, we’re sure that you’ll be able to identify it and fix the problem without having to spend money on a consultation or a mechanic! Good luck!