Chirping Sound on cold start up - Porsche 997.2

[Wheeler hogs]

Hi,

My TT has only recently started to make a chirping noise on cold start up - either immediately disappears when the engine has turned over, or I can't hear it. Can't hear a noise with the engine bay open.

Just to be clear, it is loud enough to hear inside the car, coming from the engine compartment.

Any ideas, or similar experiences?

[Fpaskell]

Almost certianly a slight slipage in the auxillary drive belt; i had the belt replaced at the last service and notice that mine now does this very briefly at start up so i suspect it is not properly adjusted.

[Rockster]

Wheeler hogs said:

Hi,

My TT has only recently started to make a chirping noise on cold start up - either immediately disappears when the engine has turned over, or I can't hear it. Can't hear a noise with the engine bay open.

Just to be clear, it is loud enough to hear inside the car, coming from the engine compartment.

Any ideas, or similar experiences?

My 996 Turbo's belt does this after a wash or when I park the car outside in the rain. If you'll look at the volt meter when you start the engne and hear the chirps the volt level is probably low since the belt is not turning the alternator. I just let the engine idle until the belt/pulley dries and the voltage reading climbs to around 13.75 volts or so (estimating since the gage is analog not digital) and then go on my way.

The tensioner may be weak but I've never encountered a weak one. I bought a new one for my 02 Boxster when I first got the car in 02 along with a full set of idler rollers and haven't had to use a one after over 265K miles. The Turbo has over 105K miles and has its original tensioner and idlers, save one which was replaced when it got noisy.

If the belt slips when dry or when you add load... flipping on the headlights concurrent with turning on the A/C then the belt drive is suspect and needs looking at.

'course just to be safe you need to check out the belt. Fine cracks across the v's are ok but there should be no missing sections of the v's. The belt's edges should be dull. If one or both are sharp the belt is rubbing and this is a sign an accessory drive pulley is out of position which in my experience came from a worn out water pump.

[tonycordon]

I had this happen to my Boxster S, I too thought it was a belt slipping momentarily and used some belt dressing to try to stop it-that didn't work. A few days later and I happened to mention it to a Porsche independant that I was visiting and he said 'Oh yes we,ve had this before-took us ages to work out that it was a slightly loose spark plug!' When I got home I took the coils off the plugs one by one and checked the plugs for tightness, sure enough the third one was very slightly slack, I tightened it and the noise stopped and never reappeared. Interestingly my 997 owning neighbour recently had a squeak/chirrup noise on start up, on my recommendation he took it to his indie who found a slightly loose plug!

[Wheeler hogs]

Thanks guys, incredibly helpful input.

I noticed the car was struggling to turn over more than usual and is accompanied by chirping noise, so these posts make sense - perhaps the battery charge was low. Seemed okay this morning but turned over better than yesterday. Will keep an eye on it

[Rockster]

Wheeler hogs said:

Thanks guys, incredibly helpful input.

I noticed the car was struggling to turn over more than usual and is accompanied by chirping noise, so these posts make sense - perhaps the battery charge was low. Seemed okay this morning but turned over better than yesterday. Will keep an eye on it

A slow to crank engine based on my experience with my Turbo is a weak battery. I've run into a couple of crummy batteries of late. (Battery quality is going downhill as I type...)

A slow to crank engine coupled with the chirping your hear could be a sign the alternator is presenting a large load as it tries to supply the power to run the car's electrical system and charge a sick battery.

If you hear the chirping every cold start right at engine start you can remove the belt and start the engine sans the belt to confirm the noise is belt related or possibly coming from a loose plug. In all my years I've never had that problem but apparently some have.

Be sure you note the correct routing of the belt and if you reuse the existing belt its direction of rotation. Take pics so you do not have to rely upon your memory to get the belt installed correctly.

While the belt is off inspect it carefully. Check each accessory drive for any play. Any play is a possible sign of a drive's bearings wearing out. Generally if there is any play the water pump is suspect but there are exceptions.

[Wheeler hogs]

A technician has told me that he has heard of instances whereby the turbos make a rattle noise on cold start up?!!

[Rockster]

Wheeler hogs said:

A technician has told me that he has heard of instances whereby the turbos make a rattle noise on cold start up?!!

I would think for the turbos to rattle upon cold start their bearings would have to be worn and the seals less effective and the exhaust would have some visible smoke. But maybe not.

A quick test, well, maybe not that quick but a test nonetheless would be to remove the serpentine belt and start the cold engine and see if the noise was present. If the noise was present with the belt removed then the noise is coming from inside the engine or it could I guess come from the turbos.

[OggyDJ]

Wheeler hogs said:

A technician has told me that he has heard of instances whereby the turbos make a rattle noise on cold start up?!!

Didn't he mean Turbo variants, i.e. those with the Mezger ? This is a rattly engine on idle anyway due to gear drives from the intermediate shaft (or something like that !!). Anyway, would think he meant the engine is rattly and not actually the turbo chargers. Might be wrong though !

[KGB1]

Another consideration is a manifold or turbo gasket, when it heats up the gap closes and the leak stops.

[Wheeler hogs]

Just heard back from the technician that it is perfectly normal and nothing to worry about. Turbos apparently make this noise. It's just odd I haven't noticed it before in 2 months of ownership until recently..........

[Rockster]

OggyDJ said:

Didn't he mean Turbo variants, i.e. those with the Mezger ? This is a rattly engine on idle anyway due to gear drives from the intermediate shaft (or something like that !!). Anyway, would think he meant the engine is rattly and not actually the turbo chargers. Might be wrong though !

If the poster was referring to the engine I agree. They are noisy/rattling things upon cold start. Doesn't bother me as I can tell the difference between normal noisiness and noise arising from something wrong.

But owners who come from cars with much quieter engines or engines that are better sound insulated can really freak out from the noise.

[Wheeler hogs]

This is the 997.2 Turbo, so not the Mezger engine

[Rockster]

Wheeler hogs said:

This is the 997.2 Turbo, so not the Mezger engine

The engine in the 997.2 while not a Mezger engine is itself a noisy engine. Some of the noise at cold start comes from the mechanicals -- DFI brings with it its own noises -- but some arises from the ... well, maybe not the best choice of words but I'm pressed for time ... lousy combustion. This is on purpose to help feed fuel to the converters where it is burned and helps heat these up quicker.

Upon a cold engine start if one listens carefully he can hear backfires in the exhaust. These are subdued due to slow running speed of the engine and the limited amount of unburned gas and air in the exhaust. The turbos, converters in fact the entire exhaust system also of course diminishes this noise. These backfires are a sign of an overly rich mixture which as i mentioned above is intended to heat the converters quicker.

As the engine warms, really as the sensors warm up and begin working, as the #2 sensors indicate the converters are working, the fueling is cleaned up -- to avoid overheating the converters -- and the engine smooths out and quiets down.

[Wheeler hogs]

Thanks for this, v useful to know.

I wouldn't consider myself to be too paranoid re engine noises, but I am aware when I hear a "new noise" and this is why I was concerned. Having had problems with previous car engines and belts slipping, crank shaft pulleys failing etc, I automatically assumed the high pitch chirping noise would be that. The main point is that I have never heard it before, which begs the question "why now?"

A technician has told me not to worry, so worry I shall not, but to be fussy, it doesn't sound particularly like I would expect an incredibly expensive lump of metal to sound when turning over....!

Rockster said:

The engine in the 997.2 while not a Mezger engine is itself a noisy engine. Some of the noise at cold start comes from the mechanicals -- DFI brings with it its own noises -- but some arises from the ... well, maybe not the best choice of words but I'm pressed for time ... lousy combustion. This is on purpose to help feed fuel to the converters where it is burned and helps heat these up quicker.

Upon a cold engine start if one listens carefully he can hear backfires in the exhaust. These are subdued due to slow running speed of the engine and the limited amount of unburned gas and air in the exhaust. The turbos, converters in fact the entire exhaust system also of course diminishes this noise. These backfires are a sign of an overly rich mixture which as i mentioned above is intended to heat the converters quicker.

As the engine warms, really as the sensors warm up and begin working, as the #2 sensors indicate the converters are working, the fueling is cleaned up -- to avoid overheating the converters -- and the engine smooths out and quiets down.

[Rockster]

Well, your familiarity with your car counts for something. If the noise is new and troubling to you it bears investigation.

Obviously I can't hear the noise so the value of my input is limited.

Your tech tells you not to worry but he doesn't offer any explanation as to where the noise is coming from and why you shouldn't worry.

To tell you not to worry is just a variation of "they all do that", which to me is a sign I should worry...

So my advice would be to seek out a 2nd opinion.

I'd like to know if the noise is coming from inside or outside the engine.

One method to determine this is if the noise is present consistently at cold start is to remove the serpentine belt and start the cold engine and let it idle just long enough to confirm the noise is present still or absent. This shouldn't take long, just seconds. You can let the engine idle longer but no need to push things.

If the noise is absent this strongly suggests the noise is from an accessory drive or a belt tensioner bearing or an idler roller bearing.

The two times I have experienced abnormal noises from the engine of my cars is with the Boxster a water pump was going out. A check for play of all the accessory drives found a small amount of play at the water pump. The belt had a sharp inner edge which was a sign the belt was rubbing and it was rubbing from the play at the water pump.

In the case of the Turbo, the noise proved to be a noisy idler roller bearing.

If the noise is coming from inside the engine -- this with the belt removed -- then that is something else.

But almost always the noise is from outside the engine.

Oh, for the belt removal be sure you note the routing of the belt *before* you remove it. Take pics. Sketch the routing. Note too which direction the belt turns and install it back the same way. Or if you want just replace the belt.