Free tier analyses the first 30 seconds of any clip. AI diagnosis isn't always 100% accurate — treat it as a starting point, not a final answer. For brakes, steering, or fuel issues, stop driving and see a mechanic regardless of what this says.
A knock sits a step up in seriousness from a tick — it's deeper, heavier, and usually gets louder under load or with RPM. The main causes are: detonation/pinging from fuel igniting unevenly (often low octane fuel or carbon buildup), rod or main bearing wear (a genuine mechanical fault that worsens over time), a failing fuel injector on diesel engines specifically, or a loose accessory like an alternator pulley that just sounds more serious than it is.
Timing matters a lot here: a knock that appears right after refuelling points at fuel quality; one that's been growing steadily over weeks regardless of fuel points more toward bearing wear.
Rod knock is a deep, rhythmic knocking sound caused by excess clearance in a worn connecting rod bearing. It typically gets louder as RPM increases and is sometimes more noticeable under load than at idle. Unlike a fuel-related knock, it doesn't improve with a fuel change — and continuing to drive on a genuine rod knock risks turning a bearing replacement into a full engine rebuild. If a knock is getting progressively worse over days or weeks rather than staying constant, treat that as the more serious possibility until you can rule it out.
Yes — using fuel with a lower octane rating than your engine needs can cause detonation, sometimes described as pinging or knocking under acceleration. It's usually a lighter, more metallic sound than a mechanical knock, and it often clears up with a higher-octane fill-up or a fuel system clean. This is a more common cause than people expect, especially right after using a different fuel station or a lower grade than usual.
Diesel engines are inherently louder and knockier by design than petrol engines, which makes a genuine new knock harder to notice at first — but also means it's worth paying attention once you do. On common diesel platforms like the Cummins 5.9 and 6.7, Ford Powerstroke 6.7/7.3, and PSA/Peugeot-Citroën HDI engines, a new or worsening knock is frequently injector-related — sometimes called an injector knock or CP3 knock — with a distinct rattly, uneven character compared to the engine's normal running noise. Fuel system issues show up disproportionately often on these platforms specifically, which is useful context if you're trying to narrow down the cause on a diesel truck or van.
This is one of the most-searched engine complaints across a wide range of vehicles — Hyundai Sonata and Elantra owners, Kia Optima and Soul owners, Chevy Equinox owners, and F-150 owners all report it commonly enough that it shows up repeatedly in owner communities, alongside diesel-specific complaints on Cummins-powered trucks. The exact likely cause shifts depending on the platform (fuel-system issues are disproportionately common on diesels, bearing wear is more of a mileage-and-maintenance-history question on petrol engines), so adding your vehicle's brand, model, and year above helps the AI weight the possibilities correctly for your specific engine.
Detonation from fuel quality, worn rod or main bearings, a failing diesel injector, or a loose accessory like an alternator pulley. Timing (right after refuelling vs. gradually worsening) is a strong clue.
Not always, but treat it with more caution than a tick. Fuel-related knock is often manageable; rod knock is a genuine mechanical problem that worsens over time.
A deep, rhythmic knock from excess clearance in a worn connecting rod bearing. Gets louder with RPM, doesn't improve with a fuel change, and risks more engine damage the longer it runs.
Diesels are naturally louder by design, but on Cummins, Powerstroke, and HDI engines specifically, a new or worsening knock is often injector-related.
Yes — low-octane fuel can cause detonation/pinging under acceleration. Usually lighter and more metallic than a mechanical knock, and often clears with better fuel.