Regenerative braking noise, This is not the normal squeak,whine,or hum

[pirajoi]

I have a 2004 Prius Pkg #9 with 45k miles. I bought it wrecked and have rebuilt it. I have one last noise that I need help identifying. I have read pages of Priuschat topics and realize there are a lot of noises that one can hear, especially if they are looking for something. Well, this one is very obvious. When one rides in my car the reaction is usually, "wow, you need to do something with those brakes"
I have done enough troubleshooting (thanks to the many helpful posts here) to figure the noise is coming from the Regenerative Braking. The noise is mostly a grinding noise, sounding like the brake pads are worn down and rubbing the rotors. I have checked the brakes, rotors, and backing plate and they are all fine.
Here are the details:
Noise sounds like it is coming from the front right wheel.
Happens when braking, stops at 7 mph.
When in "B" mode it is heard when turning the wheel to the left.
When in "B" mode it gets louder when turning left and the brakes are applied.
When in Neutral, the sound is gone.

The car took an impact to the front right wheel and the axle was replaced. There was a bad speed sensor and when I replaced it, I started hearing this grinding noise. All the Warning lights are off now. I unplugged the sensor just to see and the noise was gone until I plugged it back in. Sometimes, especially when in "B" it sounds almost like a Jake Brake from a Semi, not loud enough to wake the neighbors, but you definitely hear it inside the car.
Hopefully someone has an idea what may be causing this. It seems if it was a problem internally wouldn't there be a warning light? I have read and read, and I am stumped on this one. Any ideas?

[hobbit]

If my rotors have sat out in the wet for a while and accumulated a
little surface rust, I get a light scraping sound when regen braking
or even just driving along slowly. The contact between pad and rotor
is so light it's almost "ringing" at its natural frequency while
doing this. Falling off regen or going to Neutral tends to increase
that to a serious scrape, for a while, until the rust is rubbed off.
.
So it's interesting that you say the noise disappears in low-speed
braking or neutral, when the physical brakes are actually *used*
rather than just hanging there next to the rotors. So your diag
of it being regen-related is likely correct -- take note, this is
one thing that hybrid-aware auto techs need to keep in mind on any
braking-related noise complaints! ... but what you describe sounds
a bit more serious than delicate rotor contact, so I'm not sure I
can point you any further in the right direction. CV joint, maybe?
What exactly got damaged and in what way before you got it?
.
_H*

[IsrAmeriPrius]

<div class='quotetop'>QUOTE(pirajoi @ Nov 12 2007, 07:14 PM) [snapback]538683[/snapback]</div>

I have done enough troubleshooting (thanks to the many helpful posts here) to figure the noise is coming from the Regenerative Braking. The noise is mostly a grinding noise, sounding like the brake pads are worn down and rubbing the rotors. I have checked the brakes, rotors, and backing plate and they are all fine.[/b]

The regenerative braking is accomplished by one of the motor/generators, nowhere near the wheels.

[seasalsa]

There was a recent post from a Prius owner in NJ that has a similar problem and found that it was the caliper. Here is the link to that thread.
http://priuschat.com/index.php?showtopic=40245&st=20

[pirajoi]

<div class='quotetop'>QUOTE(hobbit @ Nov 12 2007, 11:58 PM) [snapback]538732[/snapback]</div>

If my rotors have sat out in the wet for a while and accumulated a
little surface rust, I get a light scraping sound when regen braking
or even just driving along slowly. The contact between pad and rotor
is so light it's almost "ringing" at its natural frequency while
doing this. Falling off regen or going to Neutral tends to increase
that to a serious scrape, for a while, until the rust is rubbed off.
.
So it's interesting that you say the noise disappears in low-speed
braking or neutral, when the physical brakes are actually *used*
rather than just hanging there next to the rotors. So your diag
of it being regen-related is likely correct -- take note, this is
one thing that hybrid-aware auto techs need to keep in mind on any
braking-related noise complaints! ... but what you describe sounds
a bit more serious than delicate rotor contact, so I'm not sure I
can point you any further in the right direction. CV joint, maybe?
What exactly got damaged and in what way before you got it?
.
_H*
[/b]

Thanks Hobbit
The rotors had some rust on them where it sat for a while so I had them turned to clean them up. This didn't change anything. The car did take an impact to the right front wheel. I know the axle was damaged, to what extent I don't know. I do know that the previous owner changed the axle and put a good one in it. He told me that he is confident that it and the joints are all good. He suggested wheel bearing, but I am wondering how that wheel bearing or cv joints could make a sound only during regen braking.

[qbee42]

<div class='quotetop'>QUOTE(pirajoi @ Nov 13 2007, 11:04 AM) [snapback]538859[/snapback]</div>

Thanks Hobbit
The rotors had some rust on them where it sat for a while so I had them turned to clean them up. This didn't change anything. The car did take an impact to the right front wheel. I know the axle was damaged, to what extent I don't know. I do know that the previous owner changed the axle and put a good one in it. He told me that he is confident that it and the joints are all good. He suggested wheel bearing, but I am wondering how that wheel bearing or cv joints could make a sound only during regen braking.
[/b]

My first though was CV joints or bearings. Regen braking loads both, since you are using the drive components to apply a braking force. The load is backward from normal driving, so it is possible you may hear noises while braking and not while accelerating.

Tom

[pirajoi]

OK, so I have put a new wheel bearing in it, and a new axle and the sound is still the same. I am running out of ideas (and money) The sound still sounds like it is coming from the area of the front right wheel. If I put the car in N the sound is gone when I slow down. Everyone that drives the car, thinks it's a noise in the brakes, but the brakes are fine. It only does it during Regen Braking. Does anyone have any other ideas of what it could be?

[pirajoi]

OK, so I finally found the source of the problem. The noise was coming from the motor mount on the passenger side. I noticed the vibration noise when the car was in park facing downhill so I got out to listen for it. As I rocked the car back and forth the noise dissapeared. So during Regenerative Braking it was just enough to push the engine forward enough to put the mount in a bind, and it was vibrating against itself. Pretty wierd and not something the average mechanic would even think to look for, but I am pretty glad I found it. I took the mount apart, and the ear that bolts to the apron was bent a little, I put it in a vice and bent it back and where you could see it was rubbing I ground a little off to prevent it and the noise was gone. I've not seen this solution in any other threads so hopefully it may be a help to others if they have a similar situation. Thanks for all the help and advice and I love my Prius even more now, with quiet braking.