Shrill sound from above dash are at higher speeds

[shyster77]

Dear Boxster-mates,

I'd appreciate your help very much, here.

Lately, I have been experiencing this shrill sound when the car moves at higher speeds, and disappears when the speed lowers. I looked up whistling sound, even though the sound feels more like a loose bearing spinning at high rpm, on the forums and cross-checked the following,

1) Check front hood level from bumper - hood is lower than the bumper. Should they be even?

2) Check dash trimmings - all seem to be in place.

3) Aligned and taped down the three plastic pieces which cover the battery and cabin filter so that they don't move.

4) Lowering the window or driving when the top down, doesn't seem to change the appearance of the sound or its disappearance. It seems to be only speed induced.

I have a 7 second mp4 file of this sound but am unable to upload to the site.

Any insights on what to check next?

Many thanks in advance!

Edited July 21, 2013 by shyster77

[shyster77]

Adding a few more cross-checks here,

5) Turned off cell phone and Bluetooth headset to eliminate any interference even, if the radio is off.

6) Taped over the two vents near the fuel cap to eliminate any escaping vapors leading to the sound.

The sound still exists at higher speeds.

Just curious, if any internal rattles within the dash, I can hear some rattling at really low speeds - along the lines of coming to a stop at a light, be more pronounced at higher speeds?

[thom4782]

Do you hear the sound with the AC and fan completely off? Bit of a grasping at straw here, but wondering if you're hearing refrigerant passing through the expansion valve or evaporator.

Edited July 22, 2013 by thom4782

[Richard Hamilton]

What year is your car? Early 996s suffered from loose windscreen rubber surround trims which would cause the sort of noise you describe. There was a technical bulletin on the subject, which involved packing the seal with a foam rubber cord. May be the same on Boxsters.

Edited July 22, 2013 by Richard Hamilton

[whall]

"1) Check front hood level from bumper - hood is lower than the bumper. Should they be even?"

The hood / front bumper relationship is correct. The hood is aligned lower to eliminate wind noise.

Bill

[shyster77]

Thanks, Thom.

The sound seems to be present with/wo Ac, so I'm not sure if it may be refrigerant related.

It is a 2000 986 S, Richard.

Interesting that you should mention a loose windscreen trim - my windscreen was replaced a few months ago due to an expanding crack from a rock chip. I can't recall if I have been hearing that sound since then but it only appears at >=85 mph, so can't recall driving it that much for sometime, until I noticed this a month or so ago. Would it help to insulate the insides of that trim in the area on top of the mirror or all around? Should the trim be insulated on the outside too? The sound seems to be around that mirror area.

Thanks for the confirmation, Bill.

Edited July 22, 2013 by shyster77

[rprieto]

I have the EXACT same problem! The "shrill" or high pitched noise (kazoo-like but more irritating) happens at HIGHER speeds. Mine is on the passenger side and . With the top down and @ speed, my son (sitting in the passenger seat) was able to confirm the location of the vibration, at the top of the windshield where it meets the body. He simply pressed down on the rubber portion and the noise stopped.

I've not FIXED it yet but I was thinking of laying down a thin layer of clear silicon adhesive or something under that area.

Since the freeway I seem to live on is more a "parking lot", I rarely am able to move at those speeds so I am not bothered by it often enough.

Edited July 22, 2013 by rprieto

[shyster77]

Interesting finding there, rprieto!

Let me check on that - ironically, there have been a few downpours in the Phoenix area in the past week and no leaks observed in the windshield area.

I hear you on the "not bothered by it" too, since for now, it seems to remind me to watch my speed but my concern is more if/when it may start to show up at lower speeds.

[Richard Hamilton]

Even if there was no rubber, the screen wouldn't leak, as it is bonded in. The rubber is just a filler/trim piece. Just to eliminate it as a possible source of the noise, you could temporarily stick some wide masking tape to cover the rubber (sticking to screen and body). It would stop the air getting under the leading edge of the rubber.

[shyster77]

Thanks again for that pointer, rprieto - I starting running my fingers over the panel that covers the top of the windshield in the inside of the car, feeling for any movement and Voila! - the area just a bit further away from the center (as to be read from the mirror area), seemed to have moved out a bit, snapped back into place, under a little pressure. I suspect the windshield installer may have had something to do with this dislocation.

I did a couple of runs after this and so far, that sound hasn't appeared.

Will keep you all posted after a few more runs to see if it is completely gone.

That makes sense on the leak insulation, Richard.

Let me continue a few more runs post this panel snap-in. If the sound reappears, I will pursue the masking tape approach which, I assume will be in the inside of the car.

[Richard Hamilton]

I meant on the outside of the screen - I was assuming it might be a loose rubber seal on the outside that is vibrating in the air flow. Perhaps I've got the wrong end of the stick.

[shyster77]

Got it! Will add this to my next to-do item.

[shyster77]

That sound is still there. :(

I did check the rubber seal on the outside - it is firmly stuck to the windshield and the body - no movement anywhere.

Would using some kind of insulation on the inside - where there is a gap between the glass and the body, help here?

Any other ideas on how to muffle this?

Thanks again, everyone!

[RFM]

The screen is probably not glued properly in the slot, remove the rubber seal, put another layer of glazing sealant around the window and place the rubber seal back. It would than have to be solved.

[shyster77]

Thanks, RFM!

Would this kind of silicone seal work or are there specialized ones for windshield seal?

http://www.permatex.com/products/product-categories/adhesives-sealants/sealants/permatex--clear-rtv-silicone-adhesive-sealant-detail

Edited August 9, 2013 by shyster77

[RFM]

Windshield sealant is indeed a specific product, approved for use with airbags. I would go back to the shop, which has placed the windshield, to have it redone, perhaps warranty?

[shyster77]

Makes sense, RFM.

Had a call with my insurance company who did the windshield replacement and hopefully should have it fixed soon. Looks like they are going to remove the windshield and reseal it, per the conversation.

Will close this thread once this is confirmed to fix the issue.

Thank you very much for your prompt responses here!

[RFM]

You're welcome.

[shyster77]

Update on this:

Windshield company tech listened to the video of the shrill/whistle sound that I had captured during a drive, felt the rubber molding on the windshield and almost instantly, diagnosed it to be due to the air getting trapped/moving under/around the molding. Per the tech, if the windshield was re-seated deeper with the existing after-market molding, there is a likelihood that the sound may go away, but a better longer-term resolution would be remove the windshield, reseat appropriately, and seal cohesively with a Porsche molding. So he has ordered one and hope to have it taken care of, by early next week.

rprieto, Richard and RFM - you guys were dead-on the root cause! :thumbup:

Edited August 12, 2013 by shyster77

[shyster77]

Windshield tech resealed it with the Porsche molding, sourced from the local dealer, last week.

A few test drives later, the shrill/whistle sound is confirmed to be no longer present.

Yet another case closed, successfully! :drive:

Thank you for your insights again, everyone! :cheers:

Edited August 19, 2013 by shyster77