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Porsche 997: Why is My Car Making Unusual Noises on Start Up?

Pops and bangs from your exhaust may sound good when your hammering it at 7,000 rpm, but right off a cold start, not so much. Find out why your Porsche 997/911 is sounding like an agitated popcorn maker.

By Brett Foote - May 14, 2015

This article applies to the Porsche 997/911 (2005-2012).

Do you have unusual or inexplicable noises coming from your Porsche 997/911 at various times of operation? Normally, noises aren't unusual when you consider that modern cars consist of thousands of components, but there are some that you should pay attention to. This articles goes through the more common noises that 911 owners have reported, and their potential causes. Keep reading as this article will help you track down the culprit to get things running quietly again.

Rattling or Knocking Under Cold Start

Many have reported a rattling or knocking noise when their 911 is started and the engine is cold, which can last for a few seconds. This type of noise isn't unusual for a car, especially if it has been sitting for days at a time. The root cause of the noise appears to be the air pump, which injects air into the exhaust manifolds during cold starts. This is to comply with increasing emissions' regulations. Combined with retarded spark timing and a richer mixture, the injected air causes the catalyst to light off more quickly, lowering the emissions.

Figure 1. Increasing emissions' regulations have led to the inclusion of an air pump, which can make quite a racket on cold starts.

Squeaky Noise During Start Up

Generally, a squeaky noise during start up is a sure sign of a worn or cracked serpentine belt. This noise usually goes away after a few minutes. Squeaking can also occur if the belt is too tight, or if a pulley is loose. A bad water pump will also cause a similar noise. Serpentine belts in a 997 generally last around 50,000 miles, but many have reported them wearing out prematurely.

Figure 2. A bad serpentine belt can cause a loud squeaking noise.

Tapping Noise on Cold Start

Many 997 owners have reported hearing a tapping noise from one side of the engine and another following a cold start; one that increases in repetition with engine speed. This noise generally goes away after the car has warmed up. This noise is typically caused by a lifter that is stuck, or has air trapped in it from sitting for a long period of time. Oftentimes, the lifter will fix itself by becoming unstuck or if the air bleeds itself out. If the problem persists, it may be indicative of a more serious problem, and it should be checked out by a reputable dealership or mechanic.

Figure 3. A stuck lifter or one that has air trapped in it can cause a tapping noise on cold starts.

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