—Solved 4/10/2020–

I am a Porsche newbie. I posted this in a reply on a 997 forum, but it was a convoluted thread talking about many different sounds.

I feel like I will get a better response in a new thread on the 996 forum.
It's an ‘01 996 Turbo (tiptronic) 24,500 Miles. This is my first Porsche; as such I am not sure if the rattle at 2k rpm is normal or a heat shield or something internal like a timing chain or intermediate shaft rattle?

Also, I don’t know for sure if the other, lower "whirring" sound that I hear is the normal sound of the Turbos and just muffled from the stock exhaust or a ps or water pump.(second youtube video below but similar to the before after exhaust video I found (vid #3 below)

Is the best solution for my sounds, a louder exhaust? :-)


So first off, I have a metallic rattle just before 2,000 rpm (I have posted two videos on youtube so you can hear it)
Had my son rev the car to find the sound and hold it on the rpm level.
I climbed under an expected to find the rattle. But could not easily isolate the location.
It's more on the drivers side. I originally thought it might be near the driver side turbo like a waste gate but that wasn't it. And the source was not easily identifiable, even with a stethoscope.



In the next video he rev'd up to 3k rpm twice so I could record what I describe as a "whirring" sound. You can also hear the rattle at 2k rpm (both are the same whether in park or under load in drive)




Other than the rattle is the whirring sound normal to 996 turbo? Perhaps because here is that same sound a different 996 video, in the stock sound before, and it's gone in the “after” of this video replaced by the sound of turbos spooling.
Is the best solution for my sounds, a louder exhaust? :-)

 

i can't help with a suggestion as to what is causing that intermittent metal on metal "whirring" in that 1st clip. but i can say with certainty, it is not "normal".
after listening again, it has the sound of something blade driven. turbos? water pump impeller? it sounds as if something "spinning" is briefly contacting another metal part.

 

I was thinking along the same lines. Not normal and the metal scraping sound at 2K along with the whirring makes me think it is a waterpump impeller bearing going. I would see if you can get underneath the left rear (driver side) corner and listen if the scraping/whirring sounds are louder on that side of the engine.

 

agree, and if so? given the low stated mileage on the car - it's likely that it's the original WP which ( iirc? ) had a metal impeller - which you do not want to grenade sending bits throughout the entire cooling system. why *most* of us swapped out for wp's with the composite impeller. also, a failing wp will "wobble" on the shaft.

given this is a possibility? i wouldn't drive the car at all. where is the dreaded "abs/psm drive to workshop" cel when you might actually "need" it.
this is "one" time i would absolutely drive to workshop stat, and do not pass go. GL w it.

 

It sounds like touching a screwdriver to an electric bench grinder wheel.

 

To clarify, it’s not intermittent, it is every time it passes the 2,000 rpm mark, up or down. The reason it sounds intermittent in that clip is my son was trying to hold the rpm’s on it for the sound clip.

also i am not referring to that metal noise as “whirring “. I am describing the the other background engine noise that changes pitch with rpm as the whirring. More noticeable in clip 2

 

you wrote "whirring" in the 3rd sentence of your first post on the topic. i heard "whirring" in the clip you posted and offered my best advice.

good luck.

 

I am not arguing just trying to clarify.
I am describing two different sounds. One is the rattle at 2,000 rpm. The other is the whirring that may or may not be normal as I hear what I am referring to as that whirring sound in the stock part of the fabspeed video too (video 3). And it is gone in the after perhaps the sound i am referring to as whirring is the muffled turbo spin.

 

Perhaps I should start it up tomorrow without the serpentine belt for a minute and see if it is still there?

 

Pull the airbox, remove the belt. Spin the water pump, idler pulleys, alternator and ps pump and also wiggle them to see if they have play. If you don't find the smoking gun, then start it briefly to see if the sound is gone

 

I finally made time to work on the Porsche. Took the serpentine belt off. All of the pulleys feel solid and smooth. So, I started the engine without the belt and the sound is gone. Looking close, I am pretty sure it’s the alternator cooling fins; somehow contacting the alternator body at the 2,000 rpm mark.

 

sounds and read like metal on metal to me. good for you for sorting it out.

 

If you have a manual trans. That alternator is not the right one. It should have a sprague clutch built into the pulley. Don't think it is your problem, just a point of refernce.

 

it’s a tiptronic, and the alternator was replaced 5 years before I bought the car. So it’s definitely not the original. Not sure if it’s correct for the tiptronic either.

 

The TIP does not use the clutch on the altenator.