speed related whirring

[ss2115]

Hi. The car has developed a soft whirring that is strictly road speed related.
ie: it doesn't change tone or pitch with steering, engine revs or brakes.

If i was in an older holden, I'd swear it was the speedo cable. However, the Mk3 is all electronic and the speedo is as smooth and sweet as new.

The whirring drops out at 20klms or below (doesn't fade - just ceases).
Above 20klm it starts as a lower tone and increases to a higher frequency the faster we drive. But it doesn't get louder, just higher. It is strictly in time with road speed. Its like a constant very low volume tone, with the occasional small amount of warbling just like a slightly noisy cable might sound.

Any ideas?

[Ben J]

A wheel bearing maybe?

[ss2115]

A wheel bearing maybe?

Wheel bearings usually change with cornering as different forces are applied to them. And they tend to rumble rather than have a very high frequency whine like this noise.

If you've ever had that annoying constant tone in your ear, its like that but changes up and down with road speed and isn't as loud.
I was hoping it was a small rock caught in the disc pad, but it makes no difference when braking, so its not that.

It has to be after the differential if its a drive line noise as its exactly in sync with the road speed. Anything before the diff would be changing with the engine speed instead of road speed.

Its not going to be the CV's either as it would change with cornering and it doesn't.

I thought maybe wind noise also, but its too constant and has a very steady mechanical sound rather than an inconsistant whistle.

[coops]

could be the rear brake piston is making the pads rub up against the disc, mine is doing that atm, need to push the pistons back in

[Preen59]

Rotate your tyres and see if the sound changes, moves position or goes away.

I've seen tyres wear oddly (like, some tread blocks wearing faster than others) before and sound like a wheel bearing etc.

That's just one suggestion.

[confuseddubber]

I agree with preen, my tires are doing exactly what your experencing. My bets its just noisy tires