[jblackburn]

Probably the vacuum assist pump for the brakes.

Does it sound like this?

 

[jblackburn]

jblackburn, on your video, were you referring to the sound at the last 2 seconds of the video? I think that is what I hear. I will check again tonight.

You (I) can hear it throughout the entire video when I hit the brake pedal.

If the little pump is constantly running, there's a vacuum leak to the brake booster somewhere. It should build up a vacuum, then shut off.

 

[jblackburn]

I have tracked the noise down to the vacuum assist pump.
Thanks, jblackburn. You were right.

The noise is from the vacuum assist pump. I hear the noise when the key is in START position (engine not started; brake not pressed). The noise stops after starting the engine. Then, I can hear it momentarily when I pump the brake. It stops immediately afterwards. Doesn't sound like it is continuously running (once the engine is started).

Could this be a bad vacuum assist pump? Could it be a leak? Wonder why it is constantly running before the engine starts.

If it stops once engine is started, and only runs when brake is pressed that is normal.

Running while off - I'd suspect a bad check valve in the line to the brake booster or the little vacuum "reservoir".