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That noise is a booster pump that builds up vacuum pressure for the brake booster assist when the engine is off
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If you hear it pretty often, perhaps you have a bad check valve near the brake booster leaking vacuum pressure and/or a vacuum leak in a hose somewhere. If you ever experience problems with braking in the morning with a cold engine or in reverse, take your car in immediately. Otherwise, I wouldn't worry about hearing the noise too much.
Awesome! Thanks for the quick reply jblackburn. Now I am a bit concerned after reading your reply. Mainly because I didn't use to hear it before. I can understand the booster assist providing more vacuum, but if it keeps on doing that till I start the car, I don't think that is expected. I need to check the brake test as you mentioned. The last couple weeks has been in mid three digits here (105 to 112F) but since yesterday we got some heavy rains and temp dropped to high 79F. I wonder if that would affect this any.

I will do some more data collection on this from today and report back. I sure hope nothing is wrong with my brake system. Gulp! I have wife and two little kiddos with me most long drives everyday.

Thanks again jblackburn!
 

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I can understand the booster assist providing more vacuum, but if it keeps on doing that till I start the car, I don't think that is expected.
It normally runs for 3-5 seconds and then cuts off. If you hear it running for 10-15 when you just flip the key on, something isn't holding vacuum pressure. Temperature has no effect.
 

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It normally runs for 3-5 seconds and then cuts off. If you hear it running for 10-15 when you just flip the key on, something isn't holding vacuum pressure. Temperature has no effect.
Got it! I surely am hearing it much longer since I got out of the car went and opened the hood and looked under. Still heard the sound. Came back and sat in my to start it and at that point I could still hear it till starting the car.

I will be talking to my dealership shortly, but I am afraid they will not hear the sound and send me off with the "everything's normal" :- (
I'll let you know what I find out and what happens.

Thanks.
 

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I checked out my car over lunch and definitely the sound stays on for a long time--i.e. till I started the car. Also I noticed that it is different from the brake vacuum sound in jblackburn's video. Mine seems more of a fast whirring noise.

I tested out the brakes and they seem fine.

I took a video of the sound from my car. Hope you all can see it and somebody can figure out what it is. Note that this is with the ignition key in ACC and engine not running. As you can see in the video the radiator fan is also not turning, so the sound is something else.

 

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That sounds like it is coming from somewhere around the AC compressor area (it's to the left of the turbo there).

My car pretty much sits at home, so I won't be able to try this theory out until later. Go inside the car and turn off the AC button and turn the fan speed off as well. See if it still makes the noise. Yours may be a slightly different noise of what GMTech was describing a few pages back in the thread.

I don't know where that vacuum pump is running under the hood, but I would guess it's somewhere near the back or left side of the engine bay and NOT in that area. Your noise sounds different anyway.
 

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jblackburn, while this sound is going on, the AC is switched off and the fan is OFF as well. Interestingly the radio is also OFF. The ignition is in ACC and so the dash is lit up and so are the perimeter lights.
 

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Hi rscruze

Please let me know when you decide to take your Cruze to the dealer. I can set up a service request for you and assist you in getting the issue diagnosed and repaired.

Jackie
Chevrolet Customer Care
 

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Hi rscruze

Please let me know when you decide to take your Cruze to the dealer. I can set up a service request for you and assist you in getting the issue diagnosed and repaired.

Jackie
Chevrolet Customer Care
Hi Jackie,
Thank you for your offer to help out. Unfortunately I did not see your post until today. Sorry about that. Also strange thing is that this morning I did not hear the sound. I will be listening carefully the next few days and report back if I hear it again.

That is too bad though, since I am most worried about issues like this that come out of nowhere, nobody has an answer and then disappear just like that without doing anything :(

Thanks.
 

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Hi rscruze

In the future please don't hesitate to contact me if you need any assistance. You can send me an inbox message. Please keep me posted.

Jackie
Chevrolet Customer Care
 

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Video of my cruze doing this, seems like the thermostat to me Cruze noise - YouTube



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I have attempted to chase down the source of this same sound several times from my '13 2LT 1.4L w/manual trans. To me it sounds like a pressure equalization since it fades out as opposed to an abrupt end such as if it were an electric device turning off. My theory was turbo related until reading the 20 pages of mostly similar comments including the non-turbo LS 1.8L owners w/similar complaints. That leads me to suspect A/C pressure as mentioned by others previously. In response to those who said that the noise stops with a key on/off (i haven't tested)...perhaps there is a compression bypass that activates on key-on to facilitate starting and releases any pressure. Just guessing on that.

I believe this is still unresolved since I haven't seen resolution or acknowledgement of issue from GM. Pls let me know otherwise.
 

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I have it and don't worry about it. My Pontiac Montana and Transport had it. The owner's manual for the Montana actually stated that you would hear the engine fans running after shutdown. It is part of the car's built in cool down process and is the result of various pumps and fans running to properly cool the engine. Other than curiosity about exactly what is generating this noise, this really isn't an issue.

Also, when I had the mold and mildew cleaned out of my A/C, the HVAC after-blow was turned on. After-blow is loud and can be heard from several yards away.
 

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Hi phugoff

Have you been to the dealership yet? Your Cruze should sill be under warranty. If the sound concerns you I would suggest you bring this to the attention of your Service Adviser. If you want my assistance with this at all just send me a private message.

Jackie
Chevrolet Customer Care
 

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Hey guys,

I hate to add to an already drawn out thread but I had this happen to me as well today. I had just done a short trip to pick up pizza for the work buddies and after I got out I heard it. When I pressed the lock button on my key fob the noise got quieter and then went back to the same noise as the videos that have been posted which says to me that this is electrical and probably not some pressure bleed off.

I did not use the AC today, and haven't in weeks since it has been cold out so I doubt it was the AC compressor. I was a little harder on the car with the suburban Redmond driving around microsoft. Electric related/hard driving in 60 degree temps with no AC? Maybe it is that turbo cooler motor? Sure is a loud little thing!

Figured this would help us all zero in on that square wave sounding issue.
 

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It's not the A/C system. This sound is nothing more than the various pumps in the engine running coolant around to help cool down the engine at a consistent rate.
 

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FAQ this one .....................................................
 

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Could you be hearing the brake booster vacuum pump? Ignition on/engine off pump the brakes a couple times and the vacuum pump will cycle. New recall on the micro switch that controls the pump. Can cause an intermittent hard pedal


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