Re: Whining noise - recorded sound up-loaded

Over the last couple of months I've noticed a slight low pitched whistling noise. It gets louder with speed ie. rolling down hill in neutral with the engine ticking over. It does seem to be getting louder with time. With the top up or down I'm not able to identify where it's coming from.

My manual '99Box has done 99k miles, has the original wheel bearings, the discs and pads are good all round and I have checked the transmision fluid level.

Any ideas on what it could be, or checks I can do to find the cause please?

Marty (UK) 1999 Boxster 2.5 manual

Have you made any adjustments/changes to the hood or front bumper? I believe if the hood is a bit too high in relation to the bumper cover you can get a whistling sound. (Hood edge should be slightly lower than the top of the bumper cover.)

The hood should be slightly lower than the bumper (not even). Also, if the gap between the two is not correct it can whistle. Both are easy to adjust.

- To adjust the height, pull back the carpet near the latch and unscrew the two 10mm bolts and adjust the latch
- To adjust the gap
* remove the big u-shaped plastic cover that surrounds the latch (requires removal of 4 plastic screws - 90° turn only)
* loosen the flat-head screws that go into the bumper. Shove the bumper in the direction you wish to adjust. Tighten the screws.

*** Big warning - it's tempting to check the bumper gap immediately after adjusting it. But what pops the bumper up when you pop it is the rubber protrusions on the underside of the hood pressing against that plastic piece so when you remove it it may be hard to reach around the hood to pull it up. It's not impossible, just difficult. I recommend just not latching the hood until putting the plastic back.

Relevant pictures are shown in this article on Pelican Parts:
[www.pelicanparts.com]

No, I haven't touched the bumper or hood.

Marty (UK) 1999 Boxster 2.5 manual

... even though you haven't made any adjustments the latch and locking mechanisms wear down and the hood rides up a little bit higher causing the whistle.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Easiest way to test is to put painters tape across the gap.

Put it on the left "L" gap (the fender-bumper curve to the center latch point), then on the right and you can narrow it down to the offending side. Then follow the instructions above. Just a tip.... since I had the issue and had a new bumper put on..... For whatever reason, the hood bumper/adjustment thingy on one side didn't touch the bumper threshold... it floated. I could tell by simply pressing down on the hood over the bumper. I screwed it down about a half turn a pop, then it touched, then it starts to raise the hood. Just move it a midge and take it for a ride and see if that does it.

Another source is the roof-A-Pillar-window interface. I suspect you know it is not this. If it is, then you can re-position your window by unhooking the battery for a few minutes and re-set the window stop point per instructions in your manual. If this does not work, you can "push" the window outwards (not inwards as it is counter intuitive) by loosening two nuts under the door - pop off two rubber plugs. If it is the window, let us know and we can give you more detailed instructions.

Peace
Bruce in Philly

Put a piece of tape over the overflow drain hole near the gas tank cap (temporarily) and see if the sound goes away. I had two Boxsters that had this "issue".

-Rey

Earlier this year I had a similar issue on my 2011 Saab 9-5. I went through the same checks, trim, bearings etc.. and it turned out to be the tyres. In my case they were Michelin which looked perfect but when checked were actually warped. The noise sounded like a low hum at between 50 & 75mph. I replaced both rear tyres with Continentals and the problem was gone. Hope this helps.

Right, just checked the bonnet (hood). The leading edge is below the top of the bumper cover. I loosened the +head screws under the wide plastic trim and pushed the bumper cover back as far as it will go. It was already right back.

What do a wheel bearing or trans axle sound like when they go bad?

I've just been driving and I think whistling is not quite the right description of the sound. It's more of a mechanical whine.

Marty (UK) 1999 Boxster 2.5 manual

... In the wheels generally won't whine but in the transmission they do.
See if the whine goes away when you depress the clutch while the car is under way.
Happy Boxstering
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Wheel bearings are more of a rumble.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

I tried pressing the clutch and it has no effect on the noise. I get this noise in gear and when coasting.

As my Goodyear F1 Eagle tyres have been on for several years could they be the culprit?

Marty (UK) 1999 Boxster 2.5 manual

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

I have borrowed an MP3 recorder and will try and record the noise tonight and post a link tomorrow.

If it turns out to be the carrier taper bearings in the diff (which support the short shafts to the main drive shafts) that are worn, should I get it sorted straight away? Is it a job that can be done at home with the car on wheel ramps?

Having searched the net for people with similar noises, I would revise my description to a low, whine rather than a whistle.

I have recorded my whining noise as a WAV type file:

View My Video

It was recorded while coasting down a steep hill in neutral with the engine at idle. I reached 50mph then braked gently to a stop.

Touching the brakes has no effect on the noise.

Any clues please?

Marty (UK) 1999 Boxster 2.5 manual

(I covered this and more and my lecture at BRBS a couple of years ago)

It helps to fix all variables and then selectively change each one.

Some examples,
At a (more or less) constant speed, does revving the engine in neutral change the sound?
=> if so, the problem is related to the revolution of the engine (worn belt/pulley bearing -- A/C, alternator, water pump)
At idle does the sound vary depending on the speed of the car?
=> if so, the problem is related to the wheels/suspension or the airflow
At a constant speed, does the sound vary when going around a corner?
=> if so the problem is on one side of the car (wheel bearings?)
Does the problem go away when you put the car in neutral?
=> if so, the problem is in the drivetrain (transmission?)

I realize you already answered at least one of the above.

Thanks for the help. Did the recording suggest a cause?

Reving, cornering, shifting to neutral have no effect on the noise.

Increasing the car's speed with the engine at idle makes the noise louder. Slowing down reduces it.

Marty (UK) 1999 Boxster 2.5 manual

Did the sound change when you adjusted it? Mary's suggestion of putting tape over the gap is a quick and easy test.

The evidence suggests that it has to do with an aerodynamic issue, something rubbing on the ground or moving drivetrain piece (such as a wheel), or something in the drivetrain at or after the transmission.

There also could be some other aerodynamic or body-related issue like a dragging flap or something rubbing.

One possibility is that there could be something stuck between one of the heat shields and the rotor. If that's the case, it would be louder on one side of the car than the other. You may be able to drive by an observer on one side then the other to determine this. Another way is to drive by a solid wall on one side then the other. The wall will bounce the sound back at you and amplify it.