Weird fan noise from engine compartment at start up

[Sparky]

  It will make the noise every 5 minutes or so for about 5 seconds (roughly).

 

I think it may be that electric driven vacuum pump for braking. Perhaps it is cycling to create the correct pressure/vacuum and then switching off.  Whatever it is, it is loud and sounds like something is dying. 

 

Next time someone changes their oil, just lay under the car with the under shield/tray off and listen to where the sound comes from.  Or I'll do it in about 9000 miles. 

 

I suspect a vacuum leak.  The car should be able hold vacuum overnight.  This is easily checked by connecting a vacuum gauge and watching for a drop over time.

[dtorres]

Before shutting down the car, I turn off the ac. If not, when I start it in the morning it starts in ev and it makes a buzzing sound under the hood. Turn ac off and it stops.

I do the same thing turning the A/C off at night so I don't have to hear the buzz in the morning when I start the car.

[cgul]

I have a couple of other hybrids and yes the "it sounds like a computer fan going bad" is the electrical A/C compressor running.  Another common noise is the brake system periodically priming itself to maintain brake line pressure (it doesn't run off vacuum from the engine like in a conventional car).

It does have a brake vacuum pump for the power brakes.

From the service manual:

 

Excessive brake vacuum pump noise (above 70 dB)

• Brake vacuum pump bracket isolators
• Brake vacuum pump

Verify the noise is from the brake vacuum pump. INSPECT the vacuum pump and vacuum pump bracket isolators. INSTALL new vacuum pump isolators or vacuum pump as necessary.

[C-MAXER]

It does have a brake vacuum pump for the power brakes.

 

Yes, hybrids have an electro-mechanical system.  They need an electric pump to supply the vacuum pressure when the ICE is NOT running.  If not, then you wouldn't have power brakes whenever you ran in EV mode.  Not a good thing!   :)  Look under the hood and you may notice the lack of a huge, circular vacuum booster mounted to the firewall from "the good ol' days".

 

I've noticed that the CMAX brake pump is MUCH quieter than either of my previous Toyota hybrids.  Nice touch.

[zhackwyatt]

My will buzz sometimes as soon as I touch the door handle or open the door.  Usually when I leave it in my garage unlocked I notice it.

[roninsd]

Mine, too.  I was told this was natural, a part of how the car works.  It usually lasts only a few seconds.

[grggwlkr]

Could the noise be the shutters cycling open and closed. I don't have any idea what that would sound like though. Someone posted a Ford service article that describes the shutters cycling open and closed at start up to calibrate the end ranges. I'm not sure the Ford engineers know what all the variables are that make the shutters work.  Much debate has taken place on this forum. One variable that seems to make them open is the AC being on, and them closing is the ICE temp being low.

[robertiv]

I think the sound you are hearing may be the automatic grille shutters. They are controlled by engine coolant temp, vehicle speed, and the A/C system. I believe when you start the A/C (e.g. by starting the car after leaving the A/C on when turning off the car), the grille shutters have to open. If there is no demand for the A/C, the shutters won't open until the other systems (engine temp, high vehicle speed) call for that. 

[acacio]

I am also having this issue, and I'm pretty sure it is the break pump. In the mornings, or when the car has been parked for a while, I hear the noise when I step on the brake pedal. It usually lasts about 5 seconds, but if I step on the pedal again, the noise comes back, and keeps repeating until after three or four times. 

 

My question is this. Someone posted that the service manual recommends replacement if noise is above 70dB. Does anybody know if the service manual has any mention of the distance you should measure it? My pump is clearly louder than 70dB if I stick a meter close to it. 

[ptjones]

I think the sound you are hearing may be the automatic grille shutters. They are controlled by engine coolant temp, vehicle speed, and the A/C system. I believe when you start the A/C (e.g. by starting the car after leaving the A/C on when turning off the car), the grille shutters have to open. If there is no demand for the A/C, the shutters won't open until the other systems (engine temp, high vehicle speed) call for that. 

To eliminate confusion Shutters open when you shut off the car (usually), turn on the A/C, Defrost and at 210*F WT at slow speeds(less than 55mph) or 215*F WT above 55 mph. The rest of the time they are closed. The noise you hear first must be brakes pumping up, because like you say if you put your foot on the brakes you hear the sound and will keep doing it if you step on the brakes again. Apparently shutter operation is pretty quiet. This info is covered in Grill Cover Thread. :) 

Paul