2009 GTS intermittent noise

[ILCUL8R]

Hi. My '09 Cayenne GTS (32k miles) has a bizarre low intermittent "woo woo woo" noise under these circumstances:
- No noise on start up or idle
- Doesn't happen all the time
- NOT a continuous whistle like a tea kettle
- Occurs when starting to accelerate from standstill
- NO check engine light
- NO decrease in power or mpg
- NOT a squeal like sticking disc brake
I originally thought it only occurred when vehicle was totally warmed up and outside temp was high, i.e. 80's, 90's, but it did it again yesterday in high 60's. At last oil change in April dealer couldn't reproduce sound (naturally) so it is unresolved and my extended warranty is about to expire . 
After accelerating from stop the noise will stop after a few seconds. That part is consistent. Noise also doesn't seem to be getting louder either. 
Very annoying problem. I took it for a 3 mile ride last week with the windows down, I stopped and started throughout the ride and it didn't do it even once. Now that speed was slow, around 25-30 mph versus yesterday 50-55 mph. Called dealer and they suggested may be tires cupping or something like that but they are fine and alignment is fine also. 
Anyone have any idea what this could likely be? Any suggestions appreciated.
Thanks

[wizard]

"- Occurs when starting to accelerate from standstill"

 

... after releasing your handbrake?

 

 

"After accelerating from stop the noise will stop after a few seconds"

 

.... Does the GTS have separate drum brakes for the handbrake?  Binding brake shoes?

 

Edited October 25, 2018 by wizard

[ttocs]

Along with what wizard is suggesting, do you use the hand brake? It's worth operating it - gently - at low speed as just a "what if" to see if it produces the noise.

 

Otherwise, maybe check the wheel bearings.

[ILCUL8R]

Thanks for the suggestions. I don't use the handbrake. On the Cayenne it's actually a foot emergency brake and I believe it's part of the rear disc brake assembly, not a drum. Anyway, the wheel bearing idea also is a possibility. I have an appointment next week with a different dealer to try and resolve this mystery. Plan to take a drive with a technician and hopefully it will happen when he's with me.

[Loren]

4 hours ago, ILCUL8R said:

Thanks for the suggestions. I don't use the handbrake. On the Cayenne it's actually a foot emergency brake and I believe it's part of the rear disc brake assembly, not a drum. Anyway, the wheel bearing idea also is a possibility. I have an appointment next week with a different dealer to try and resolve this mystery. Plan to take a drive with a technician and hopefully it will happen when he's with me.

 

The parking brake on a 2009 Cayenne GTS is a drum brake inside the rear rotor hub.

[ILCUL8R]

Sooooo, took GTS to local dealer, rode with tech for a few miles on straight, curving and thru some roundabout roads and it made it's noise again. He felt is was "rotational". Left it with dealer. Next day I picked it up and tech told me he found that the back plate just behind the left front rotor was slightly bent at one spot which he bent back to shape with the correct gap. He drove it for 20 some miles and couldn't reproduce the noise after that. So it seems when brakes heated up that bent spot was close enough to just tick the back of the rotor enough to make the strange woo woo sound. Yeah!! Happy camper now.
Not sure how it was bent unless it was when new tires were mounted more than a year ago, or when brake flush was done this past April. Very bizarre.

[ttocs]

Excellent news!

 

Earlier this year I had a noise that wasn't always repeatable. It only happened on very hard right bends, like on on-ramps to highways. Mine might be a lesser version of what yours was. I had concluded that my noise was just reflected sound. But now . . . . might be worth checking into further. Thanks for posting this!

[ILCUL8R]

Yes great news, BUT it happened again last Sunday night after driving for approx. 20 minutes. Was approaching a red light that turned green before I got there and as I accelerated again got the infamous noise again. BUT it only happened ONCE. Porsche tech told me that if it happened again to really get on the brakes and that might clear up any deposits on the narrow gap between the back plate and the rotor. Have to try it when I'm out next time in the right place to try it. He also told me that the sensors are getting close to new brake "time"  and maybe one of them on the driver's side is nicking the rotor or pad , who knows. Bizarre !! 

[GSpence2]

My bet is wheel bearings

[Tats]

Diagnosis can be difficult for wheel bearings - the standard grab the top / bottom and rock the wheel or feel for roughness rotating often doesn't work especially if they're big bearings. If want another method of checking, getting the appropriate number of wheels in the air with the car in gear so things are under drive (make sure you do this safely so the car doesn't drive off without you.....) and touching the spring gently can give you a diagnostic - you can feel a slight pulse being transmitted by a rough bearing. I re-emphasise, these are 4wd vehicles, so jacking up one wheel will be insufficient. Diffs could be locked too etc etc, and the wheel will be spinning so....please be safe. No loose clothing, watch straps, long hair near anything spinning etc etc.

[ILCUL8R]

So here I am back again almost 3 years later with the same issue. The symptoms are the same as before except for one thing I've noticed. When the whooping or low whistle noise occurs, if I tap the brake it disappears and if I let off brake while still rolling forward it re-appears until I get up to 20-30mph. Now the tech at local Porsche dealer went for a ride with me and heard the noise.  (He doesn't believe it's a wheel bearing issue as the sound is nothing like that and it disappears when up to speed.) He initially thought it could be a leak or crack in vacuum line going to booster pump and what we're hearing is air escaping until more air is forced into it when brake is engaged. BUT now after looking at it in the shop he thinks the large engine cooling fan is skipping intermittently and that could be the noise. He ran engine at idle with hood up and the noise was louder and then disconnected fan it stopped. Ok, i guess could be that , but what i can't understand with that is how does tapping the brakes stop the noise if it is the fan ?? 

Any thoughts or ideas appreciated as usual.

Edited August 28, 2021 by ILCUL8R
Added more info