Dr_Strangelove

Also check the rubber seal around your window glass (front and rear, sound can do wacky stuff..)

When this happened to me it was the clear film on my driver's side mirror had started to peel just slightly and had created a harmonic vibration at speed. Disappeared completely when I peeled it off.

TahoeGaper

I do have very dated, likely 3M protective film on my hood and mirrors- that could be the culprit Now that I have the Fister exhaust the hmm is not so bad ;>)

jasper

So this exact thing has just started happening in my 2002 996 with 281km kilometres on the clock. The noise starts about 120 kmh , stops and starts but does not change pitch and it stays pretty consistent at 140 kph.

Not engine speed dependent at all. I put in the clutch and coasted at 140 kph downhill and the whine stayed constant.

My old clear bra is in tough shape, but I don't think there are any floppy edges....I've been slowly trying to remove it in fact and it is on there really solid. Will check though..

Noise sounds like it's coming from behind center dash vent..hvac on or off. Windows open or closed...

Did you ever figure yours out OP?

Fishah

Interesting... I have a 40 AE and get this also but only between 95 and 115mph. High pitched whine from dash... So odd.

Dranon

I regularly drive my car at 85-90 on the New York State thruway! I was just down in Florida and drove my Hyundai Venue rental 85-90 on the highway between Daytona and Orlando several times! Getting 37 mpg!!

Putt-Putt

This might be dumb but is it possible it's coming from spinning from speedometer or other gauge cluster component? Pbly not, right?

Fishah

In my case no chance, it's very loud. Downs out the radio.

jasper

Another threads talked about it being a window seal issue and sure enough I had mine changed recently and they installed a one with a more rounded profile.

I ran some experiments last night with painters tape and it looks like this might be my issue. Hard to get up to those speeds multiple times to run the tests so not conclusive yet.

TahoeGaper

OK so here was my situation- Same humming from the dash area when I would be at 85 MPH the hmm would start. One day I figured out that the below- Windshield Cowl Cover was broken at the passenger side. I has cleaning the window and leaned on it and it moved a decent amount. I found this thread on Rennlist and it was huge help: https://rennlist.com/forums/996-foru...placement.html

WindshieldCowlCover 996-572-563-06-01C
Right CowlCover Screw Cap 996-572-569-01-01C
Left CowlCover Screw Cap 996-572-570-01-01C
WindshieldCowl Gasket 996-572-931-00

Fishah

Interesting thanks for the post. My cowl cover does seem pretty solid but I'll check it out.

Interestingly I did notice that one of my wipers seems to have an air deflector and the other does not. Could this be related?

jasper

My cowl cover seems ok too, but will absolutely run a test with it removed if the window seal issue doesn't pan out.

Thanks for the tips guys.

TahoeGaper

So mine was broken at the plastic area around the screw- for reference.