What is that mechanical whine noise in the front?

In the front sometimes I hear a fairly loud whine, I thought maybe a fan or maybe battery? My first Prius, it jumps on all of a sudden and turns off in a minute. I was thinking of having the dealer check but it just maybe part of a hybrid system.

Is it when you are driving and applying the brakes? If so it is the regenerative braking and normal. If you received the DVD from your dealer, it explains it and other noises you may hear.

Read your post again. This noise should not be loud. You may want to take it in to be safe.

I believe what your hearing is part of the Hybrid System and nothing more. I hear it as well, more so, when in close proximity of cars and or the garage or anything that will let it reverberate. It's totally normal IMO, if you don't have any warning lights your most likely good. This is my 2nd Prius and I noticed a few new noises but they all appear to be normal from the manuals, DVD, and information I have gathered over time.

The other day I turned off the car, locked the doors and there was a noise at the rear and I believe it's part of the High Volatage system...again all normal.

But if concerned, by all means take it to your dealer and have them listen.

There are two electric motors under the hood, and the whining you hear is probably associated with them. When braking, it'll sound like a subway car or train coming to a stop, with a winding-down whine sound. THe opposite when speeding up.

We can't hear your "whine" though and it may not be the same as what we're used to. It could indicate something wrong.

EDIT: When do you hear the whine? Does it get louder/softer, higher/lower-pitched?

If you hear it just after turning the vehicle off I think that might be the system pumping some of the engine liquids into a thermos to keep them warm(ish) in case you come right back out and start the car up again. That way you don't waste energy reheating that stuff.

No thermos on the GEN III, no bladder in the gas tank either, and no belts to replace.

The whine you hear is likely the sound of the two electric motors spinning down under regenerative braking ... and is heard as a decreasing speed whine when you are approacvhing a stop.

As for the poster who mentioned the pumping of coolant into the thermos bottle ... the 2010 doesn't have that.

Are the lack of these a good thing? As in less things to break down over time and need to replace?

I would presume so. I never owned a GEN II, so can't comment on the thermos. The bladder was used to get the CARB emissions rating, but it caused refueling issues; Toyota figured out how to get the emissions rating in a more traditional approach. And no belts to break or need to replace is a good thing.

flux capacitor?

No... that's positioned slightly above and just behind the front seats.

Besides what people suggested here, could it be the electric AC compressor?

The compressor on the 2nd gen can get pretty loud and does vary in speed. There's also a fairly loud noise when it activates.

my salesman told me, when i ordered the car, that the genIII's have a thermos.


this is why i come here to get the truth.

Does it sound slightly metallic?

Well knock me over with a feather! A salesman who doesn't know the product...



Certainly there is no thermos on the GIII

This sounds possible something to do with the AC and fan maybe. I didn't hear it today. Maybe like a big box computer whine like a DVD loading or cooling fan with a slight whistle to it. I don't think anything is broken I just like to know whats going on.

Do you hear it when you open the driver's side door when the car is parked? If so that's the brake pump (to increase the brake fluid pressure so the power brakes work). There's a post by htmlspinnr on this, but I couldn't recall where I read it.

Thats a sound I was also wondering about so that clears that one up. No I think this sound is when the car is running and driving.