For the most part a whining noise in your car is going to be made by something in the engine compartment. The likely cause will be determined by when you hear the noise.
With that in mind, this page is divided by when you hear the noise, and common causes of the whining noise under those conditions.
Before you go any further, is the whining noise constant when you rev the engine? Or does it not change with engine speed? If it changes with the engine, it’s most likely going to be an accessory bolted to the engine (or the radio, shut it off and see if it stops). If it stay constant as you rev the engine it’s going to be something else.
Car Making Whining Noise When Accelerating
A whining sound when accelerating is almost always caused by a bad engine accessory. Here are the most common causes of whining noises when accelerating:
Bad Serpentine Belt
Your car’s serpentine belt is responsible for taking the motion from the crankshaft, and using it to turn all of your accessories. When it goes bad, it’ll cause a high pitched whine. This is particularly true when you first start the vehicle.
Bad Alternator
When an alternator is going bad, it’ll often begin to put out a high pitched whining sound. It should also be accompanied by the battery light. If not, it may not be the alternator making your car whine.
Power Steering
The power steering pump is a very common reason why your car might whine when accelerating. If it gets too low on fluid they’ll make the car whine a lot. You need to check the fluid level and fill it back up to the factory fill line.
The pump can also go out. To determine if it is the power steering pump, turn the wheel left and right with the vehicle sitting. Does the sound get louder while turning? That’s a great indication that it is probably the power steering pump making noise.
Water Pump
When the water pump goes bad, it’ll make a squeaking sound. It’ll often sound like a deeper whine than a bad alternator.
Car Whining When Starting
Whining when starting can be frustrating to diagnose, since you constantly have to start and restart the vehicle to duplicate the conditions that caused the sound to begin with.
Here are the most likely causes of a car whining when starting:
Radio
The radio can accept interference and cause noise when starting the vehicle. This is a great place to start, since it only takes a second. If this does stop the noise, there’s more on this directly below.
Starter
The starter may not be fully engaged with the flywheel/flexplate. Or, it could be a situation where it is having a hard time disengaging. If it is even a little bit out of alignment, it’ll be enough to cause a whining noise.
This is the most common reason that a vehicle makes a whining noise when starting, but it is not necessarily the only one.
Transmission
A bad torque converter can cause a whining sound when starting your vehicle. A good place to start would be to check the transmission fluid. You’re going to want to check it for both color, and metal content.
If you see any flecks of metal on there, it is probably going to need serviced. As long as you have the dipstick out, go ahead and check the transmission fluid color. It can tell you a lot about the health of your transmission.
Car Stereo Making Whining Noise
If the stereo is making a whining noise, it is usually caused by a condition known as “alternator whine”. Alternator whine is a product of a drop in voltage between the radio and the alternator itself. It is usually way more noticeable on the A.M band of the radio. You’ll hear it match the acceleration of the vehicle.
Alternator whine is almost always caused by a corrupted ground wire to the radio. Once a good ground is restored it should go away. Here is a great page with way more info on the subject.