There are various possible reasons why a car makes a humming or whirring noise as these sounds could be a sign of a bad bearing in the steering system, water pump or alternator. Faulty air conditioning systems may make a similar noise as well, especially if there is a problem with the serpentine belt, which can get stretched and worn out. The tensioner may malfunction as well and defective air conditioners usually have more of a buzzing noise, particularly when the system is overcharged or when liquid refrigerant enters the compressor.
Cars make other similar noises when a part is malfunctioning. If a car starts to make a low drone sound, much like the sound of someone blowing across the top of a soda pop bottle, this could be a sign of the motor mounts or exhaust system being worn out.
Suspension failures will make a low groaning noise, and a bearing failure in the engine or a flat tire are known to cause a loud roaring noise. Muffle rumbling noises usually stem from when a car drives across warning tracks on a highway. Mufflers can also make this type of noise. Cars can also make a high-pitched whining noise, and this may stem from problems with the air conditioning, mismatched gears in the transmission or not enough lube in the manual gearbox. Cars can make more types of sounds when a problem occurs. When in doubt, it's recommended to take a car to a certified mechanic to find out if there are any issues that need to be fixed.