Very high pitch noise, seemingly unrelated to engine speed

mazda
mazda3
noises

#1

Hi Everyone,



There is a very high pitch whine/whistle coming from the engine compartment. I’ve been able to narrow down what I can and can not do to influence the noise.



My car is an automatic.



- The noise first becomes apparent once the engine has been warm for ~15 minutes. If everything is cold, no (audible) noise.

- Accelerating makes the noise go away. Letting off the accelerator and coasting will bring the noise back.

- Turning off the engine the noise will fade out (lowering in pitch before finally stopping). Starting the engine immediately after this brings the noise back.



- Revving the engine while not in gear has no effect on the noise.

- Car speed seems to have no effect on the noise, it is present when stopped as well. Could be mistaken on this one.

- Shifting into neutral has no effect on the noise, at rest or moving.



I can’t think of anything else. I haven’t tried turning the wheel while stopped to see if steering has any effect.



Anyone have any ideas? Thanks for any help!


#2

This is a bit confusing. First you state that the noise is unrelated to engine speed, and then you tell us that the noise goes away when you accelerate, and returns when you allow the car to coast. That seems to me as if the noise does relate–to some extent at least–to engine speed.

Anyway, here are two random thoughts on the issue:
A leak in a vacuum hose?
A loose manifold?


#3

You’re right about that. When in gear and under power, the noise does seem to go away. And I haven’t noticed the noise at highway speeds. When in neutral, the engine speed then seems to have no effect on the noise, but only in neutral. Thanks for seeing the disconnect there.


#4

Like VDC I was thinking vacuum type leak - air whistling through something. Based on your description it sounds like it should be around at idle. Have you actually tried to locate the noise? Popped the hood? A piece of hose to fish around sort of like a stethoscope may be of some use.


#5

Yes, the noise is certainly there at idle. I had the hood open a couple of days ago. But I couldn’t locate where it was coming from. Between the very high pitch, and my recently punctured eardrum, it wasn’t going to work. Using a hose sounds like a great idea though. I’ll give it a try this weekend.

Thanks for your help!


#6

The fist thing I can think of is to ask if the radiator cooling fan is run by a separate electric motor, not a belt? If so that may be a good place to start.


#7

I am having a very similar problem, but I’m driving a 2004 Jeep.

Same basic issue, same basic symptoms. It’s loudest when the accelerator is not being pressed, but the amount of acceleration doesn’t seem to have much effect - meaning the sound is sort of ‘dampened’ by the act of acceleration, but not necessarily connected to the specific speed.

I had it checked out and the result was a belt replacement and adjustment to the belt arm (don’t recall the technical term) that did nothing to change the noise.

It is not constant in that it gets worse in colder weather, sometimes it’s not there at all, but if I drive long enough it can be pretty loud. Much louder outside the vehicle - I notice especially at tollbooths that it can get very loud.

The sound is a whistling, which makes me think of air leaking, and it’s central under the hood and close to the dashboard side of the engine compartment.

Any thoughts would be most appreciated!


#8

I had nearly the same problem on my wife’s 93 Olds Cutlass. It turned out to be the radiator cap. It was a Stant with a large aluminum disc on top. The disc vibrated after the engine was hot and whistled like crazy. I left the radiator cap on but I destroyed that lousy aluminum disc after prying it off.