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Noises in a Car

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Preamble

Last week we read about odours in a car. Since it's a piece of complex machinery in motion, some noises are inevitable even though today's cars are a lot quieter than their decade old siblings. Some of these are normal where as some are like coming events...
Unfortunately, an average owner-driver is unable to distinguish between the two. So let's try and explore these.

1) Normal Noises

To qualify these, let's take the noises a new car makes when you first drive it as 'normal' - assuming it didn't have any defects. These can be broadly subdivided as relating to - i) Engine/Transmission, ii) Suspension, iii) Under chassis and iv) Body/doors/panels.

First types will be lowest when the car is stationary with engine idling. Such ones will progressively go up depending upon - a) engine rpm and b) road speed. In the former category, 'refinement' of the engine/transmission design and 'build-quality' holds the key whereas in latter, 'rolling noises' depending on tyre/tread pattern vis-a-vis road surface AND the front/rear Suspension Design gain prominence.

2) Abnormal Noises

Keeping in mind that 'all aluminium' engines are noisier than cast iron block types, it's interesting to note that all the refinement of engine/transmission design can go for a six if the rolling noises predominate at higher speeds, in some makes from as low as 20 kph upwards. To a large extent, narrow footprint tyres preferred by OEMs due to better fuel efficiency are mainly responsible for such rolling noises, closely followed by faulty suspension design that leads to 'structural resonances'.

On the engine/transmission related noises, even in a healthy engine excessive 'valve/tappet clearances' can add significantly to the noises it'd make. In addition, faulty foundations of engine/gearbox too can add to them. Besides, 'peripherals' like drive belts, water pump, AC comp., power-steering pump and alternator bearings too can get noisy, with impending failure. It should be kept in mind that any engine/gearbox/accessories will get noisier as they get older/wear out.

Over and above, the most common noises in Front Wheel Drive Cars are from wornout 'axles'. Every FWD car has two of them and each has two very hi-tech 'Constant Velocity Joints' at its either end, covered with Synthetic Rubber Boots and packed with special 'Moly' grease within. Normal life of such CVJ's in our conditions is ~ 60,000 kms PROVIDED their SRB's don't suffer any premature failures as is quite common on our grit-laden roads, especially during the rainy season. Once that happens, the special grease escapes from the CVJ/SRB's and dirt gets in - leading to the CVJ getting damaged in no time.

The rattling noises a wornout CVJ makes are quite characteristic and as a thumb rule, the lhs ones are the first to give way for understandable reasons. If an Axle rattles while turning, even on take off from standstill, it's the 'wheel-end' CVJ that's gone. On the otherhand, if such rattles are heard on accln. or de-accln., then it's the 'drive-end' CVJ that's wornout.

In such situations, it's wise to replace the entire Axle assy with an OE part for lasting relief, though expensive, as regardless of what one may advise it's next to impossible to satisfactorily re-furbish such hi-tech CVJ's in the after market.

3) Suspension Noises

These can be broadly classified as - i) Soft 'thuds' and ii) Rattles. When the soft thuds become louder and occur without much provocation, as going over small potholes, one's Shock Absorbers will need looking into. If there are 'squeaks' emanating from under-sides, it'd be various Suspension Rubber Bushes that'd need attention. Normal life expectancy of such parts on our kind of roads is ~ 50,000 kms and that too if the car is driven carefully.

Rattles, on the other hand, signify some things loose or mis-aligned with car's under-sides. Most common culprit is the exhaust line that's either damaged due to a hit or unsatisfactory repairs done while replacing a muffler etc.

4) Steering Noises

While some 'soft ones' are inevitable especially on our kind of roads due to the inherent 'multi-link' nature of such mechanisms, when they get louder and manifest without much provocation that one needs to attend to them.

Such noises can arise either from loose or wornout - i) 'ball-joints', ii) 'rack and pinion' assy incl its 2xguide bushes, iii) unbalanced front wheels and iv) steering column bearings/bushes and/or its 'universal joints'.

Logically, these should wear out time/distance wise in the same sequence as above but lapses in their manufacturing quality or assembly can create exceptions. Above all, fair amount of skill is needed in identifying the real culprits coz every thing out there is so 'inter-connected'.

5) Doors and Windows

Such noises are perhaps easiest to locate for a layperson and can afflict even a new car. From doors, they're due to their mis-alignment with the body frame or excessive slack in their locks/latches. Ill-secured door panels too can vibrate and make noises. On other hand, window glasses tends to 'chatter' if not fully raised or lowered - unless their guide 'channels' are wornout due to age - usually beyond 3-years.