jliang

Hi all,
I've been chasing this problem for months now, read all the threads, tried a bunch of fixes, and the issue is still there. I would really appreciate any input before I give up and send it to a shop again for inspection.

The Problem
There are two issues that I think are present on my car (and I say 'I think' because it is entirely possible these are normal noises and I've just been chasing my own tail).

• The first is that I get an audible, consistent, fairly high-pitched whine that is linked to engine RPM. It begins becoming audible at 3000RPM, and increases in pitch throughout the rev range. Holding an RPM will hold the pitch of the whine.
• The second is that whenever I apply throttle, then quickly back off, my engine makes little knocking sounds. This is different from the exhaust burbling which I know is normal. With the belt off, it sounds like a bit of rattling. With the belt on, it sounds more like a faint ticking. I've had a tech listen to this and he claimed it was normal, and to be fair it hasn't changed in months, but it does seem strange to me.

My Troubleshooting
I have done the following troubleshooting steps to try and isolate where it is:

• Rev the car under load to 3000RPM - whine is there. Base case.
• Rev the car in neutral to 3000RPM - whine is there. Load agnostic. Likely not suspension or wheel bearing related.
• Rev the car in each gear to 3000RPM - same whine there for each gear. Gear agnostic. Likely not internal gearbox related.
• Rev the car with clutch in to 3000RPM - whine is there. Likely not clutch, throwout, or gearbox related.
• Remove serpentine belt, rev car to 3000RPM - whine is sometimes there? I took a few videos and I can hear it in some and not in others. Not super conclusive.
• Replace water pump (most common advice on threads I've read) - whine still persists. Not WP or Thermostat.
• Replace belt, idlers, and tensioner pulleys (second most common advice I've read) - whine still persists. Not idler bearings.
• Check Power Steering fluid. Within acceptable range (albeit on the low side of the range), no evidence of leaks, PS pump doesn't groan when I turn hard. Maybe not PS?
• Alternator and AC pulleys spin freely, no play. Probably not these? Not sure how I can isolate.

At this point I am totally at a loss as to where even to look next. I want to believe that my testing proves that the noise is 'normal' (or at least nominal for my car) but something in me can't bring myself to believe that. A lot of the videos I see online have the exact same noise as I do and they all had some magical fix that worked for them but when I try, doesn't for me.

I've attached an uncut video of me driving and doing various RPMs to recreate the sound. A couple example instances happen at around 00:20 - 00:28 and 0:44-0:48 but there are many throughout.
What do you think, guys? Am I crazy? Just stupid sensitive to noises? Or is there a more insidious problem going on? I'm pretty close to taking it to a tech again, but having them tell me "mmm yeah it sounds normal ish probably, each car sounds different lol" doesn't quite give me the peace of mind I'm looking for.

I appreciate all of your time and input.

VWLooseNuts

Yep i think you're crazy and just chasing your tail Just turn the radio up or open up the exhaust it will go away then lol

That said. These are not off-road cars 3:20

hueyhoolihan

didn't hear a thing out of the ordinary.

...now the noise in MY car is real, of course...

audi49

Likewise I don’t hear anything unusual. To me Boxsters (at least) have a bit of a unique whine sound to them. I found 986s a bit louder with this type of sound than my 987.

zuch

To eliminate all of the belt connected components, remove the belt. Run the car for a couple of minutes and see if you still have the noise. Don't run it too long though.

SFZ GT3

See the title of this reply. Maybe it's not mechanical at all. Since it is very independent of any driveline situation OTHER that RPM, maybe it is electrical/electronic?? Have you done any audio mods? Replaced the alternator? Aftermarket alarm, dash cam, etc.? Electrical interference through the ignition will always correspond to engine rpm.

Next time, turn off the audio and any electrical accessories or controls and see what happens.. Probably a SWAG, but who knows??

jliang

Thanks for all your input guys. Good to know the general consensus is that it's benign. Wish I read these replies before today though, as I just dropped it off at the shop to get it checked out. I'll report back with their answer when I have it/

I can hear it over the radio sometimes but that exhaust is a good idea And trust me, I wish the roads here were more on-road than off-road but I live in CA where who knows what happens to our tax dollars. Pothole central haha.

Thanks for the input! Is the noise in your car car-related or perhaps occupant-related?

Thanks for the insight. Interesting anecdote re: the 986S and the 987. I wonder if it's the engine (3.2 vs 2.7) or the better sound insulation in the newer car. That being said, if the 986S M96 engine is whinier than the M97 that could explain why my particular car is noisy, seeing as it's an early-run 987 with the 'older' engine. It really is a unique whine, almost like a supercharger or a straight cut gearbox.

Good idea. I've done it a couple times and I believe the sound goes away, which is what led me to chase after the serpentine-related parts. One thing I didn't try is remove the belt, replace the cover and carpet, and take that for a very brief drive just to remove other variables out of both tests. Oh well, maybe the shop will do that and report back to me.

Very interesting idea. I can't say I've explored too much of this but I did briefly toy with the idea of it being electrical. The radio makes a whine when nothing is playing but it's not as loud and sounds oscillatory, almost like a fast PWM signal switching on and off.

I have done no audio mods, a dash cam is there but wired to the cigarette lighter circuit, not the audio circuit. There's also very little noise that comes through in the dashcam video compared to my phone video, which I would expect to occur if that was the cause of the whine. I have not replaced the alternator either but that's another suspicion of mine. I have driven the cart with the radio on, turned down, and off, with no change in noise. Also the same with fan control on and off, as well as eco/AC on and off.

When I get the car back I'll know the answer for sure, and if it happens to be audio related you might want to buy a lottery ticket

Again, gents, thanks for all the insightful replies. I'll update this thread with the answer from the shop.

RennHarry

I hear the sound in your video very clearly. I also vote for a component on the serpentine. However, I'm not a Porsche owner, just a regular guy who occasionally wrenches.
Cheers

jliang

Thanks for that. Glad it's not just me. I also agree with your diagnosis that it's something on the serpentine circuit.

jliang

Update from the dealer: they believe it's the alternator. When I asked them if it was the overrun pulley or the alternator/pulley together, they answered that it was the entire alternator.

I checked again yesterday and lo and behold, the overrun pulley was seized on the alternator; it wouldn't allow the alternator to freewheel the non-driven direction. I also noticed grease streaks radially from the bearing race, so I believe it might've just lost its grease over time and eventually heat-seized due to lack of lubrication.

This is an interesting failure mode to me compared to the symptoms. Intuitively I'd think that a seized overrun pulley would only whine or squeal during a rapid deceleration of the belt after acceleration (ie. when the clutch is supposed to let it freewheel) like a big upshift or blip. However, the whining occurs all the time. Can the internal needle bearings in the alternator unit itself fail? When I spin it by hand the alternator is super smooth and very quiet. I wonder if the seized pulley damaged the alternator by shock-loading it whenever there was a rapid change in belt velocity.

Either way, I have an overrun pulley on its way and I'll update this thread when that gets installed. If the pulley doesn't work, I'll buy a new alternator and return the pulley (thanks FCP!)

Appreciate all the help you guys have given me so far! Great community.

SFZ GT3

See....it was electrical after all...just like I said. LOL . Glad you got it figured out, and hopefully no more "whining" regardless of the source. Keep us posted.

jliang

Haha, does it count as an electrical failure if it's a mechanical failure of an electrical part? I guess I can give it to you Electrical master
Edit: You literally verbatim said, "replace the alternator" in your original post so I have to concede you're some kind of wizard. Incredible.

General update, installed the overrun pulley today and no dice, still whining (although it seems quieter? might just be a mental thing. If it is quieter, I guess we're on the right track). I guess it's time to buy an alternator. Hopefully that solves it, I'm pretty close to giving up if it doesn't lol

audi49

Please continue to keep us posted on your findings. I personally think that 'these engines' have a whine to them regardless... at least every 986 or 987 I've driven has some whine to them. But I could be wrong, and it would be great to know if an alternator fixes it in this case... useful info! Thanks.

islaTurbine

Same for me. I’ve owned my 996 for 7 years and she’s always had a whine to her engine (M96).

hueyhoolihan

"the whole alternator".... sounds like a dealership service department's response. haha