* Low Oil Pressure: Insufficient lubrication can cause parts to rub against each other, resulting in a knocking sound. Check your oil level and pressure immediately. Low oil pressure is a serious problem and should be addressed *immediately* to prevent catastrophic engine failure.
* Rod Knock: This is a serious problem. It indicates damage to the connecting rod bearings, which support the pistons. This usually sounds like a rhythmic knocking that increases with engine speed. It's a costly repair, often requiring a rebuild or engine replacement.
* Main Bearing Knock: Similar to rod knock, but involves the bearings that support the crankshaft. This is also a severe issue requiring major engine work.
* Wrist Pin Knock: This involves the pin that connects the piston to the connecting rod. A knocking sound here often has a higher-pitched, more rapid clicking sound.
* Piston Slap: A relatively less serious issue, piston slap is caused by excessive clearance between the pistons and cylinder walls. This often sounds worse when the engine is cold and diminishes as it warms up. It can be caused by wear, or using the wrong type of piston.
* Valvetrain Issues: A lifter, rocker arm, or pushrod problem can create a ticking or knocking sound. This might be less severe than a bottom-end problem (rod/main bearing knock).
* Loose or Worn Timing Components: While less common to produce a *knock*, these can produce a rattling or ticking sound.
* Detonation (Pinging): This is a sharp metallic ping or knock, often caused by improper ignition timing, low-octane fuel, or excessive engine heat. It can damage the engine over time.
* Insufficient lubrication (from bad oil pump or clogged oil filter): The oil pump is responsible for pushing oil throughout the engine, and a bad or clogged filter limits the oil's ability to reach critical parts.
What to do:
1. Check your oil level and pressure immediately. Low oil pressure is an emergency.
2. Listen carefully to the knock. Try to determine the speed and rhythm of the sound; this helps in diagnosing the source.
3. Consult a mechanic. This is crucial. A proper diagnosis requires a professional inspection and possibly further tests. Ignoring a knock can lead to irreversible engine damage.
Ignoring a knocking engine can result in catastrophic engine failure, which is extremely expensive to repair or replace. Get it checked out by a qualified mechanic as soon as possible.
