BMW 740i Noise from engine or exhaust Inspection at your home or office.

Common reasons for this to happen:

Here’s a guide to engine noises and some potential causes.

Whirring

Description: A vibrating or buzzing, much like the sound a window fan makes when turned on.

Cause: A whirring sound that changes in relation to engine speed could indicate trouble brewing under the hood. There are a myriad of possible causes, typically on belt driven accessories or the belt(s) themselves. Your mechanic will start by listening to the bearings of your alternator, idler, and tensioner pulleys. If no problem is found, the water pump is a likely culprit.

Hissing, Gurgling, and/or Sizzling

Description: Hissing sounds like air or steam escaping from a pipe or hose. Sizzling is like a slice of bacon in a hot griddle.

Cause: These three sounds often go hand-in-hand with an overheating engine. The hissing means your cooling system has possibly developed a leak. Gurgling sounds like a coffee pot percolating, and is the result of coolant boiling (which is abnormal in a properly operating system). Sizzling is the result of that coolant or oil landing on a heated engine component like, say, the exhaust manifold. The best course of action is to pull over as soon as safely possible, let the engine cool down and call a mechanic. If the car isn’t overheating but is still hissing, other possible maladies include a clogged exhaust and catalytic converter, but these are usually associated with more noticeable problems driving.

Loud Exhaust Note

Description: We are not talking about a throaty, grumbling, wonderfully musical exhaust note. No. We are talking about loud noises that occur unintentionally and suddenly.

Cause: The most likely perpetrator here will be a broken muffler or exhaust pipe. If a loss in performance accompanies that noise, then the problem is likely something deeper, possibly a cracked exhaust manifold or broken catalytic converter.

Backfires

Description: A blast from an M-80. Technically, a backfire is fuel detonating outside the combustion chamber. It can occur in either the intake system or the exhaust system, depending on the cause.

Cause: The most common is moisture or water in the fuel system. While your car’s gas tank may be tightly sealed, H2O can still seep in as the result of condensation caused by changes in humidity and/or dramatic swings in outside temperatures. The fuel filter should remove it, but some water can get by, especially if the filter is old. An unbalanced air-to-fuel mixture is the suspect of interest here, and may be from leaky vacuum hoses or a malfunctioning air intake valve.

Sputtering

Description: Imagine a jerking action from the engine and/or powertrain. The engine indiscriminately loses power, or rpms fluctuate, as the driver accelerates.

Cause: An incomplete combustion event. While this doesn’t sound dire, it can cause serious damage to other engine components, specifically catalytic converters. On 1996 and later models, a misfire will typically be accompanied by a flashing check engine light.. Have the technician check the ignition system, not just simply replace the spark plugs. This includes examining the ignition coil, rotor, cap, and wires (if so equipped).

A blocked or malfunctioning fuel injector will also cause your car to sputter. In some cases, it may be accompanied by a steady clicking sound.

Tapping or Clicking

Description: Imagine the sound made by a watch's movement or a ratcheting wrench. It’s a metallic tick, as though someone is striking the inside of the engine block with a metal stick in a rhythmic manner.

Cause: When tapping is engine related, it is usually more pronounced at idle, and increases in speed with engine RPM.. It may disappear at high speeds. In this case, it is probably upper valve train or tappet noise caused by either low oil pressure, excessive valve clearance or a defective hydraulic valve lifter.

The most common cause -- and easiest to remedy -- is that the engine is low on oil. Another answer is that there is some blockage in the system. Culprits could include a worn or damaged oil pump or a clogged oil filter. If you haven't had your oil and filter changed in a while, consider doing so immediately.

If it's not an oil issue, it's potentially related to the valve train, as we stated above; i.e., a serious internal engine problem that is preventing normal oil pressure from reaching the upper valve train components.

Spark Knocking (Preignition)

Description: A light, metallic knocking sound, usually under acceleration.

Cause: Knocking is most commonly attributed to improper ignition timing, lean air/fuel ratio, overheating, or improper fuel octane level.

It's a common misconception that there are benefits to using a higher-octane gasoline in your vehicle than the owner's manual specifies; however, using a lower-grade fuel can very well produce engine knock.

Bearing Knock

Description: Bearing knock is typically a deeper tone, directly related to engine RPM.

Cause: It is typically associated with excessive main bearing clearance (a regular, rumble-like knock), worn connecting rod bearings (sharp, irregular knock).Bearing knocks usually involve labor-intensive repairs. The good news is, regularly performed preventative maintenance (oil and filter changes) will typically prevent bearing damage from occurring for the life of your vehicle.