Coasting, turning and just like that: where did the hum in the car come from?
Buzzing is an unpleasant thing. Sometimes it appears gradually, and the owner subconsciously gets used to it and does not pay attention until something falls. This is bad, so it is advisable to put your ears above your head at the first sign of ringing. That is, at the moment when it only seems that something is buzzing. A good buzz, of course, will come out on its own, but it’s better not to let it happen.
The hype we’re talking about today is buzz for everyone. This is not a whistle and a squeak from under the hood, which we have already written about. This is a different sound, it is not heard from under the hood, but somewhere below, on the side, or in general it is not clear where. But almost always in motion.
Therefore, the first sound is the simplest.
The most common cause of hum is worn or broken wheel bearings. It is very easy to distinguish this hum from others: in the initial stage, it occurs only at a certain speed in a rather narrow range (for example, 40-60 km / h or 90/110). It is easy to make sure that the bearing is buzzing. You just need to check if the sound changes as you turn. If it changes (disappears one way and gets louder the other), then it’s definitely a wheel bearing. The loudness of the hum usually does not depend on the degree of pressing the accelerator pedal, but strongly on the speed. In general, everything here is very simple and familiar to many.
The second fairly common cause of hum is the howl of the gearbox (we are talking about a manual gearbox). It is much less common than bearing wear (after all, the box is not a consumable item, although for some reason some manufacturers do not know this). In the box, the input shaft bearing wears out faster, and it is not difficult to verify this malfunction with sufficient accuracy. You should listen first to see if the drone’s tone changes when you increase the speed in one of the gears. If it changes, then after picking up speed, you have to turn in neutral and turn a little by inertia (just in case, I warn you: this is dangerous). If there is no hum in neutral, then welcome to the service.
A hum may appear in a mechanical box due to the fact that the oil level has gone. Most often, it will first be in higher gears (fifth or sixth), so if there is a hum only in these gears and it disappears when switching to lower gears, it would be useful to check the oil level. Or at least make sure there is no oil leaking out of the box.
Of course, the gearbox can hum for other reasons (for example, if the gears are already very worn out), but it is difficult to diagnose by ear here.
And again the transmission
In general, the transmission has most of the parts that can hum on the fly. And since they are quite rigidly connected and are able to transmit vibrations and sounds very noticeably to the body, localizing the hum of the transmission can be difficult. However, let’s try.
A growing rumble during acceleration on a rear-wheel drive car may indicate a lack of oil in the rear gearbox or its wear. And if you’re lucky, the gimbal cross and its outer bearing may buzz. But such situations are quite rare (unfortunately, we have almost no honest rear-wheel drive cars), so let’s get back to front-wheel drive.
A hum similar to the squeal of a wheel bearing is emitted by another: a transmission outboard bearing. Not all cars have it, but if there are wheel bearings in the norm, it makes sense to check. Usually the pitch of this sound is higher than the hum of the din. And it’s harder to diagnose. However, you can try. The tone often changes depending on the load on the unit, so you need to play around with the throttle. If the sound changes in any way depending on the position of the accelerator pedal, the outboard bearing is likely to be worn out. In addition, its wear is often accompanied by vibrations in the steering wheel or its runout, which also changes with acceleration.
Well, another source of noise at speed is the CV joint. In addition, the internal CV joint, which is also a tripod, buzzes more often (in most cases, the internal hinge is structurally tripod). Unlike the outer CV joint, the inner one cannot break so brilliantly when cornering due to the small angle of change in the position of the shaft relative to the box, and it is not always possible to calculate it under strong acceleration with the steering wheel turned out. Therefore, it is more difficult to manage it and it is better to do it on the elevator. If this sounds incredibly difficult, you can try moving forward at low speed and then back. If a noticeable click is heard at the beginning of the movement, the CV joint is most likely faulty. And, of course, he will almost always be out of order if his boot breaks. True, it is rather difficult to see the inner boot of a CV joint without a lift or at least a viewing hole.
And now a moment of sad information for owners of cars with a gun. The hum of a classic torque converter box usually comes from the torque converter ("donut"). True, in this case, other symptoms of its malfunction can often appear. For example, the vehicle may accelerate unevenly or twitch under engine braking. It is, of course, difficult to self-diagnose an automatic transmission, especially by ear, of course, but if there are significant changes in the behavior of the car during acceleration and braking (especially in the city) and something is buzzing somewhere in the legs, there is a good chance to repair automatic gearbox. This is especially true for those whose cars like to abuse the lock in all gears, starting with the first. There, the coatings wear out faster, contaminating the oil quite intensively. And if this oil is not changed, then the "steering wheel" will die, and then the rest of the box. But let’s not talk about sad things.
The variator buzzes much more often than a classic automatic transmission. Its rumble is often called "trolleybus" – the sound when picking up speed is very similar to the sound of an accelerating trolleybus. The appearance of such a buzz on a car with a CVT is very upsetting. And most likely expensive. Therefore, it is better not to finish the cones, but to quickly deal with cheaper repairs (for example, replacing a belt or chain), which (perhaps) can still help save the cones themselves.
But what if you don’t stream? What else could be causing the noise?
The most likely reason for a good transmission is the exhaust system. Its rumble is a bit like the rumble of a wheel bearing, but unlike the latter, the exhaust hums not at a certain speed, but at a certain engine speed. If you accelerate and release the gas, then the bearing howls in the same way and the exhaust system should be quiet. We have already talked about what can give a voice in it and will not repeat it (spoiler: most likely a corrugation or a resonator). This sound, of course, is not as dangerous as the howl of a wheel bearing, but it can be quite annoying.
Speaking of which, there are a few reasons for the hype that may not bother you. For example, on the highway, when the wind direction changes, something can also buzz (spoilers, visors, even wiper leashes). Of course, this is not dangerous and there is no need to be afraid of it. The main thing to remember is those gusts of side wind that make the car buzz – these are strong gusts and it’s not worth flying along the highway “by all means". Side wind is dangerous, especially gusty and on slippery roads. It’s better not to risk it.
We talked about what is buzzing under the hood (power steering pump, air conditioning compressor, bearings, rollers and everything else that spins). Usually these sounds are not heard on the track. But some "motor" rumble should make you think. For example, the valve membrane of the crankcase ventilation system may hum. Here you need to understand why. Well, if the membrane itself is simply worn out and torn (although this is also bad, but for new machines it is forgivable). The reason can be much more serious: from leaky VKG tubes to a worn piston and wear-related increase in crankcase gas pressure.
One last thing: often the reason for a high is simple, but not obvious. For example, a hum may appear after a "replacement" of tires. If the rumble is louder than usual, check the balance and first make sure the tire changer has not mixed up or mixed up the tires by placing them against the rolling direction. You never know, anything can happen.