Holden Captiva Pricing and Specs

Noises are impossible to diagnose without actually hearing them. So you need to take the vehicle to a mechanic and get the car to produce the noise you’re reporting. That may involve leaving it overnight or otherwise reproducing the circumstances under which it misbehaves. Experienced mechanics can often tell whether a noise is important or just wear and tear, and act accordingly.

For the record, your mystery noise could be anything from a worn turbocharger, a sticking hydraulic lifter, piston slap, bearing knock or even something as weird as a loose baffle in the exhaust system. All these things can manifest as random and metallic noises, and they range from simple to catastrophic in magnitude.

For a start, you might find it’s neither of those things causing the noise. You may have a worn tyre, poor wheel alignment or a faulty brake, to name just a few possibilities. That said, both your suspects are likely contributors to this type of noise.

In any case, there’s a simple way to tell whether a noise is coming from the driveline (engine and transmission) or from one of the wheel bearings. Drive the car at whatever speed is necessary to make the noise appear. If it gets louder as you apply throttle, there’s a good chance it’s driveline related.

But now, with the car still making the offending noise, drop the transmission into neutral (where it’s safe to do so, of course) and let the vehicle coast. This takes all the stress off the driveline and the engine should return to idle. If the noise is still present, then you have a wheel bearing or other problem linked to the wheels, brakes or axles, but not the engine or gearbox.

It’s certainly strange behaviour and your theory that because it works perfectly some of the time, it’s probably not terminal is a decent one. If something internal was broken or worn out, the transmission wouldn’t work at all. Which leads any mechanic to suspect you have either a gear selection problem or an electrical glitch.

Scan the car electronically to see if any fault codes are thrown up. But also check for things like bad earths or blown fuses and relays. You can’t rule out a major internal failure until you get inside the gearbox itself, but starting with these simple things can help eliminate other possibilities. You may find the ECU (the computer than controls the driveline) is the culprit, and is having random melt-downs.