2001 SL2; 62000 miles

Lately, at random times when the car is going 34-40mph, there starts a whistling noise that seems to be coming from the front-left wheel. My wife described is as a tea pot that starts boiling and, when I heard it myself recently, I have to agree: that's pretty much what is sounds like. Strangely, when the brakes are applied, especially to the point of bringing the car to a stop, the noise goes away. On restart (e.g., light turns green), the noise sometimes starts up again right away; sometimes it waits until the car gets to 30-40mph. Again, applying brakes seems to kill the sound, if temporarily.

When the sound is happening, and the accelerator is released and the car slows on its own, the "whistle" pitch decreases slightly. I say this to point out that the sound is closely tied to the wheel rpm.

As a mechanic myself, I've never herd brake going south making this noise, nor a wheel bearing. The usual wasted-pad sound is a metal-on-metal grinding. Most failed bearings go thump/thump/thump (though I have heard electric motor bearings give a sort of whistling sound when the bearings go).

I pulled the drivers side wheel and the rotor doesn't look too bad. There's definitely pad on the outside; the inside appears to be pretty worn.

So, any thoughts on what could be causing the whistling tea pot sound?

Does any one have the tolerance for the rotor thickness?

Thanks.

 

The following figures are in inches:

Front disc thickness * --> 0.710 inch
Minimum after turning --> 0.633 inch
Discard thickness --> 0.625 inch

Maximum allowable scoring depth --> 0.060 inch
Maximum lateral runout --> 0.0024 inch
Disc thickness variation --> 0.0005 inch

* If different specifications are cast into the disc, they supersede this data

 

Thanks for your reply, OceanArcher - especially the great details on the rotor specs. Nicely done!

As to the noise, did you have any hunches on that?

On another forurm, a guy suspected an axle support bearing or a seal.

Does this make any sense?

It also occurs to me to raise the front end and run the car - to force the noise.

P.S.
When I had the front end up on jack stands, I noted that the gear change lever was stuck in Park. Does this surprise anyone? What mechanism made this happen (i.e., did something "know" the front end was lifted, or that the wheel was removed? Just curious ...

 

I have to admit, even though I have experienced a front wheel bearing failure in the past, as well as totally worn brake pads, I cannot deduce the cause for a "whistling sound"

 

Here's a wild one:
I heard anecdotally that some cars have a sensor that detects pad wear and causes this whistling sound when the thickness is dangerously low (i.e., almost needing a brake job). In particular, I heard that some of the Nissans have this feature.

This morning, I called Saturn service and ran this by the guy I spoke with. He said that there should be a mechanical device that "senses" when there's ~20% of material left in the pad. It responds by releasing a kind of "squeal". I suppose my "whistling" noise may, in fact, be a "squeal"

Does anyone know of this feature of the Saturn SL2 - that what I'm hearing is actually a sensor noise?

In a day or 2, I plan to:

1) run the car up on stands to try & replicate the noise
2) pull the wheel again, check the rotor tolerance (thanks again to OceanArcher), and pull the caliper for a much closer inspection.

 

its possible the squeelers (sure your brakes are the same as mine as all the Sx's use the same part numbers for the front brakes) might be barely making contact causing it so you may want to check it out

 

Be aware -- that if you run too many miles with your 'squeelers' sounding off, they will make a groove in your disc rotor, making it unservicable