If you own a car for any reasonable length of time, you will get to know its idiosyncrasies quite well. You will be used to all the different noises it makes, the odd strange smell here and there and how it performs generally. More often than not, these odd sensations go away by themselves, but if you've noticed something more persistent coming from the back of the car, you may need to take action. What's back there, and what could be going wrong?
Narrowing It Down
Essentially, you have two different areas to look at when it comes to the rear of the vehicle. You could be encountering some suspension issues, or, more likely, it's to do with the differential. This is a very complicated piece of equipment that goes through a lot of wear and tear during its life. Consequently, it's one of the parts that is most likely to give you some concern.
How the Differential Works
The differential (in the case of a rear-wheel-drive car) converts the power that is created by the engine into a driving force by switching its direction through ninety degrees. The crankshaft of the engine is essentially connected to the driving shaft that turns the road wheels through this system. The entire operation is made more difficult due to geometry and the fact that the wheel on the inside of the car is turning at a different speed to the one on the other side whenever you round a bend.
Within the differential casing are many different gears, all of which have sharp teeth that interlock with each other during various stages. These gears have to be oriented and angled correctly in order to function.
What Could Be Going Wrong?
As mentioned, the differential components are under great strain, and occasionally the gears can chip away or even jump out of place, giving rise to some very strange noises and eventually leading to breakage. You can sometimes tell what's going on by the type of noise that you're hearing.
What Type of Noise?
If you can hear a low-down, rumbling noise, this indicates that the bearings that hold the gears in place are starting to wear. If the noise is intermittent, it could be the pinion bearings, whereas if it's consistent, it's more likely to be the carrier bearings.
Alternatively, if you only hear the noise when you're turning sharply in one direction or the other, it could be that the wheel bearings (which are on the road wheel end of the drive shaft) are failing.
Banging noises could be one of two things. The limited slip clutch within the differential (which is the component that allows the two wheels to turn at different speeds) could be wearing out, or the spider gears could be broken.
Sometimes, you will notice a howling noise, and if it's during acceleration, it means that the gears may have jumped out of alignment. If the noise comes during deceleration, then a component of the pinion bearing could be coming loose.
Getting Special Help
If any of these problems are affecting your vehicle, you will definitely need a mechanic to intervene, as certain types of tools are required to disassemble and fix these pressurised components.