Knocking Noise Over Bumps: Suspension Causes to Check
Written by Petro Olekhnovych, mobile mechanic in Aylesham, Kent
Kent's back lanes and winter potholes are hard on suspension. A knock that starts after a cold snap or a run down a broken village road is very common. The trick is working out which part is making it, because many suspension noises sound alike from the driver's seat.
Rule out the simple things first
Before worrying about the suspension, check the easy stuff:
- Empty the boot and door pockets. A loose jack, spare wheel or toolkit can knock surprisingly loudly.
- Look for a loose spare wheel clamp or rear parcel shelf.
- Listen whether the noise is metallic and tinny, which often points at an exhaust heat shield, or a deeper thud.
The common suspension causes
Anti-roll bar drop links
These short links connect the anti-roll bar to the suspension. When the ball joints in them wear, you get a light, hollow knock over small bumps and speed humps, often more on one side. They are one of the most common knocks we find.
Bushes
Rubber bushes cushion the joints where arms bolt to the subframe. When they split or perish, you hear a thud and may feel vague steering or a shimmy under braking.
Top mounts and bearings
The top of each front strut sits in a rubber mount with a bearing. A worn top mount can clunk over bumps and creak or knock when you turn the wheel on full lock.
Shock absorbers
A worn shock may knock internally, leak oil down its body, or let the car bounce and float. Worn shocks also lengthen braking distances.
Broken coil springs
Springs often snap near the bottom coil, usually in cold weather or over a pothole. Signs include a sudden bang, a corner sitting lower, a scraping or clonking noise and sometimes a tyre being rubbed by the broken end. More detail is in broken coil spring symptoms.
Ball joints and track rod ends
These are in the steering and suspension. Worn ones knock and can make steering feel loose. They are safety critical and should be checked without delay.
Need a service or brakes doing?
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Labour £30 to £50 per hour depending on the job. Send your reg number and we will reply with a price before any work starts.
Clues that help narrow it down
| What you notice | Points towards |
|---|---|
| Light knock over small bumps, one side | Drop link |
| Clunk when turning on full lock | Top mount, CV joint |
| Car bounces after bumps, oily shock | Shock absorber |
| One corner sits lower, scraping | Broken spring |
| Knock with loose steering or wandering | Ball joint, track rod end, bushes |
A rumble or hum that changes with speed is more often a bearing than suspension. See wheel bearing noise symptoms if that sounds closer.
Safe checks you can do
- Park on flat ground and look at the car from the front and back. Does one corner sit lower?
- Shine a torch into the wheel arches and look for an obviously broken spring or oily shock absorber.
- Check your tyres for unusual wear on the inner or outer edge.
- Note when the knock happens: speed bumps, cornering, braking or turning the wheel when parking.
Please do not crawl under the car or lift it on a jack alone to look. Suspension parts store a lot of energy and a car on a jack can drop.
When to stop driving
Stop and get help if the car pulls hard to one side, the steering feels loose or clunks when you turn, a corner suddenly drops, or a tyre is rubbing on something. These suggest a broken spring or a worn steering joint, and carrying on risks a loss of control. If the knock started after a pothole strike, our guide to pothole damage in Kent covers what to check and how to report the road.
Does it affect the MOT?
Yes, it can. Excessive play in joints and bushes, broken springs and leaking or ineffective shock absorbers can all lead to a fail. A knock is worth sorting before your test, and our common MOT failures guide shows how often suspension appears.
How we can help
At your home, we inspect springs, shocks, drop links, bushes, ball joints, track rod ends and top mounts safely on proper support, and check for play in the steering and wheel bearings. You get a clear explanation of what is worn and how urgent it is. Suspension repairs are not on our confirmed list for every car, so we will tell you after the check whether the job can be done on your driveway. Labour is £30 to £50 per hour, and we quote before any work.
Message your reg and postcode to WhatsApp 07563 350335 or use our contact page.
Need a service or brakes doing?
Message us on WhatsApp with your reg and postcode, or use our contact form, for a price before any work starts.
WhatsApp for a free quote Call 07563 350335 Contact form
Labour £30 to £50 per hour depending on the job. Send your reg number and we will reply with a price before any work starts.
Frequently asked questions
What causes a knocking noise when going over bumps?
The most common causes are worn anti-roll bar drop links, tired bushes, worn top mounts, failing shock absorbers and broken coil springs. Loose items in the boot and exhaust heat shields can sound similar.
Is it safe to drive with a suspension knock?
A light knock from a drop link is usually not urgent, but it should be checked soon. If the car pulls, wanders, sits lower on one corner or the steering feels loose, stop driving and get it inspected.
Will a knocking suspension fail the MOT?
It can. Excessive play in ball joints, bushes and links, broken springs and leaking shock absorbers are all MOT items, so a knock is worth checking before the test.
Can potholes cause suspension knocking?
Yes. A hard pothole strike can break a spring, damage a link or bend a component, and the knock may start straight away or a few days later.
