Why does my car squeak when I go over bumps?

When it squeaks tells you the cause, which is why the timing is worth pinning down before anyone touches the car. A squeak or squeal when braking is the brake pads — either the wear indicator telling you they're getting low, or brake dust and glazing. A squeak over bumps that follows the road texture is worn suspension: ball joints, control-arm bushings, sway-bar links or bushings, or aging struts. A squeal that rises and falls with engine RPM rather than road speed, often loudest on a cold startup, is a worn or loose serpentine belt slipping on its pulleys. A squeak that rises with vehicle speed and changes as you turn left or right is a dry or failing wheel bearing. And a squeak only when you turn the steering wheel is power steering or a suspension joint. The single most useful free test is to rev the engine in Park: if the squeak follows engine RPM, it's the belt or an accessory; if revving does nothing, it's almost certainly road-speed related — brakes, brake hardware, suspension, a bearing or the body itself — and you'll find it while driving. One caveat worth knowing: a belt squeal is worst cold and under load, so repeat the rev on a cold start with the air conditioning on before ruling the belt out. Get the timing right and you've cut ten causes to one or two before spending a dollar.

It depends entirely on the source, and the squeaks range from monitor-it to fix-immediately. A brake wear-indicator squeal — a light, high-pitched squeal that's present when you're not braking and stops when you press the pedal — means your pads are getting low but aren't critical yet, so drive to a shop within a week. A grinding rather than a squeak when braking is different and urgent: that's metal-on-metal contact damaging the rotors, and it should be fixed immediately. A belt squeal is usually safe short-term, but a belt that fails can leave you without power steering, charging, and cooling all at once, so it's worth fixing within a week or two. A suspension squeak over bumps is usually safe short-term but worn suspension affects handling, so inspect it within a couple of weeks. And a wheel-bearing squeak or hum that's getting louder shouldn't be delayed, because a failed bearing can develop play, overheat, and in severe cases seize. So the rule of thumb is that a brake squeal or a suspension bump-squeak can wait a week or two, a belt squeal should be handled within a week or two because it can strand you, grinding brakes need immediate attention, and a growing bearing hum should be seen promptly.

A squeal that's loudest on a cold startup and when accelerating, and that rises and falls with engine RPM rather than road speed, is almost always the serpentine belt. The belt drives the alternator, power steering pump, water pump, and AC compressor, and when it's worn, glazed, loose, or the tensioner is weak, it slips against the pulleys and squeals — especially when cold, because the belt is stiff, and under load, because accelerating, turning the wheel, or switching on the AC all make it slip more. There's a quick free test that confirms it: with the engine running, briefly turn on the AC or turn the steering wheel to full lock, and if the squeal gets louder, the belt is slipping under the added load. A second test is to rev the engine in Park — a belt squeal follows the RPM, while brake, suspension, and bearing noises don't. The fix is a new belt, usually $100-$300 installed, and possibly the tensioner, since a weak tensioner will make even a new belt slip. Because a failing belt can eventually leave you without steering assist, charging, and cooling at the same time, a persistent belt squeal is worth addressing within a week or two rather than ignoring.