Hi all,

New to the hybrid world. Just bought a used 09 Sierra 4x4 and am trying to get used to the hybrid sounds. One iv particularly noticed is on start for a few seconds, i notice a humming noise from beneath the hood. It's longer on cold starts and goes away in 10 or so seconds. Kinda sounds like a pump priming or something. Does it some on warm starts too but not as pronounced or as long. Is this normal? Or, something I need to go to the dealer for. It only has 28 k miles and bumper o bumper until march of 13.

 

There are a pair of coolant pumps in front of the engine and behind the radiator fans. They can be heard for several seconds after key off too. If it is them. There have been transmission oil cooler lines that touch the frame or body, they can make noises.

Engine running when heard?

 

Yes it is when the engine starts. I have also sort of narrowed it down to where it is louder or longer
Lasting when foot is depressing brake when the engin is started. Would that make it easier to explain?

 

Hi H,

Usually the best way to diagnose these things is for you to take a short audio clip and post a youtube link ... that way if someone has experienced it before they can identify it.

Cheers!

 

If the movement of the brake pedal makes it come on, it could be the ABS pump building pressure. The ABS pump is on the drivers side under the floor under the drivers seat.

From Auto-Stop (quiet EV) in park, pump the pedal several times. You will hear and possibly feel the ABS pressure pump. If that is not the noise, HyHoe's advice is still best here.