Toyota Prius: "Squoot" noise when pushing on brake pedal

We took a trip with our Prius and while away from home, I discovered that
every time I pushed on the brake pedal, the car reacted normally but made a
small (but noticeable) "squoot" noise that I believe was coming from under
the hood. The noise stopped as soon as we returned home - and on a
subsequent trip the noise has not returned.

Anybody else heard this?

Thanks,
Chris

Chris Shearer Cooper wrote: 

Chris: Just returned from Mammoth Lakes. Left Ventura at close to sea
level, arrived at cabin at 9,000 ft elevation ... averaging 46.5 mpg
with wife, luggage and inflatable kayak. Got 50.5 mpg on return trip.
Anyway, had same noise as you describe while in mountains. The noise
occurred at exact point of electrical actuation while depressing pedal
- point where brake lights come on. Noise came from front right side
of engine compartment. The noise disappeared after we left Mammoth
and has not returned. Also had screeching from radiator transfer pump
(where hot water transfers to thermos at time of shutdown) on two
occasions. That sound also disappeared by time we are were down to
4,000 ft elevation where we stopped for lunch. Neither noise has
returned. I called dealer today. They referred me to Toyota
engineering in Torrance. They quickly logged a case number and
promised to get back to me within three days. If you want me to let
you know their response, let me know you email address. By the way,
what did your dealer say? ... Bob net