High pitched whine @ 100km/h

[stefcio007]

I'm starting to get a high pitched whine when driving exactly 100km/h, around 2500 rpm.
If I briefly take my foot off the pedal the whine completely goes away. All other speeds appear to not induce any whining, including above 100km/h.
Any idea what this could be?

[dylan8]

If you go at 2500rpm in other gears does it do it?
When I installed my new shifter the cables rubbed on something and made it sound like it had a wild supercharger

[stefcio007]

It does sound like that, I thought it was the intake so checked it and tightened it up.
Doesn't do it in other gears.
I replaced the intake today (not because of the issue though ) so we'll see if it's still there.
It could be just some rogue airflow, I remember a similar issue on another car that was caused by roof racks aerodynamics.

[dylan8]

Check where the cables go under the fire wall and where the exhaust heat shield starts. I wobbled all that around and it seemed to help.
Might be when you select 5th everything just moves enough to hit and when you get to 2500 rpm everything vibrates in just the right way

[stefcio007]

I should probably point out that I have an auto and 4 gears...

[dylan8]

Ah, my bad

[stefcio007]

Had a listen while out today. Seems to be fairly consistent and speed does not seem to be a variable.

[Red9N3gti]

Gearbox related?

That would be my major concern. Does it do it as soon as you settle into cruising speed? Or is it as soon as you get into "4th" or top gear at 100km/ hr.

Basically does it do it straight away or does it wait until things sort of "align" into the "perfect storm".

If it's gearbox i would be suggesting age as the main culprit. A cheap solution would be changing the oil. It can't hurt, and it might give you a better idea where the noise is or isn't.

Keep us posted.

[Red9N3gti]

^gearbox oil that is

[wai]

Sounds like gear whine. This is why when you lift off, the noise goes away or reduces as the gears are idling.

If this is in top gear, it is likely to be the ring gear and pinion in the differential.

It might be worthwhile checking the transmission oil to see if it is low, or if there are bits in it that shouldn't be there. The oil will have the effect of dampening the sound.

Now all gear drives will cause some degree of noise. Straight cut gears are the worst. and this is why helical gears are used. They are less noisy, but greater power losses. The designers have to trade off noise vs power loss. So there will always be some noise. It is a case of making sure everything else is OK.