Knocking noise from a front wheel - second gen Prius

Hi all,
The Prius is 2nd gen (2009) with 67K on it now.
I have this noise I'm having a hard time explaining to the mechanics at the
dealership, perhaps because it has started right after the latest service when they rotated the tires and replaced the oil in the front differential.
I can describe it as a rather soft knocking sound that seems to be coming from the passenger side from wheel, with the frequency of once per revolution (or twice - it turned out to be very hard to drive, count and look at the passenger side wheel at the same time :) - need a huge mirror for that!) . Well, it starts soft but becomes harder and I can even feel it of the steering wheel after long and highway speed drives.
I brought it down to the dealership and they claim they could not find or hear anything but the tire and the wheel look OK (tires almost brand new - about 5K on this set yet, balanced before first installed), brake pads and the disk look fine and no foreign objects. So, they said, it's safe to drive and don't worry too much.
My wish for this noise to go away didn't materialize and I think it's getting worse. So, I decided to ask for suggestions in this esteemed group before bringing it to the dealership again. What do you guys think it can be? If not the wheel/brakes, could there be something in the suspension that can make such noise? The timing it started is very suspicious - could they have screwed something up in the front differential while changing the oil there? Else could they have bumped the wheel against something while rotating the tires?
Any suggestion and comment you can offer will be most welcomed!
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Le 11/12/2012 20:08, passerby nous fit lire :

Once per revolution... hmmm... of the wheel or steering wheel ? If the wheel itself: Check the tire, every section of it, on the rolling band. You might have a screw or bolt incased in the outer part of the tire. visual inspection should be seconded with manual inspection: pass your hand softly on the tire, all over the part that get in contact with the ground. (afterwards, you're good to wash your hands). You should have to move the car at least thrice if you do not remove the wheel. Use a mark on the side of the wheel to ensure you do not look always at the same spot. (For easier spot, turn the steering wheel full way if possible)
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replying to Le Forgeron , passerby wrote:

The wheel, going straight. Actually, not sure if going in a circle would make a difference - it only becomes obvious at about 15-20MPH and I've yet to find a circle large enough to try that.

Thank you for your suggestion. I had it down at the dealership where they claim they took it off and checked the tire. But come to think of it now: I would rather check it again myself. They did say it's safe but I would feel much better if I've seen it myself.
Despite it being synced with the wheel rotation (once per revolution), could it still be something other than the tire?
Thanks!
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Le 12/12/2012 22:08, passerby nous fit lire :

It could. On another car (not even a Toyota), I once met the same symptom (1 clong per revolution). Turn out it was the ball bearing of the wheel that was faulty (and expensive to replace) (might be due to a chock of the wheel against a sidewalk). Check is harder: rotate the wheel while it is off the ground (so the car must somehow be suspended ... the apparatus to change a wheel with the fifth wheel (if any) is not secure enough, do not do that alone). Free rotation of the wheel made it clear: clong every revolution.
Might be hard to perform on the front wheel (neutral N mode ?)
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replying to Le Forgeron , passerby wrote:

So, I did lift the wheel up with a tire jack and rotated it by hand while on neutral. Then did it with the other one just in case. *Nothing* at all out of the ordinary. I mean, I don't look at Prius wheels every day, but there was nothing embedded in the tire, no tears on the tire or the rubber gaskets, no sign of any oil dripping, nothing obstructing the wheel or could possibly come in contact with the wheel, nothing seems lose. I've taken pictures of both wheel wells while they they suspended, just can't quite figure out how to post them here.
And, no noise! Well, if you rotate them *very* slow, something in the transmission appears to start biting and the wheel jerks while you're rotating it. You can hear tiny "ticks" when you do that but not once per revolution, more like 100 times per revolution. I think it's how CVT is working although I cannot be sure.
Anyway, this time the car was cold while I was doing it, I'm going to try to do it after driving it 20 miles later today. perhaps something will change when it's warm.
So, I'm still looking for ideas. One that I was pondering myself: could the wheel be unbalances so badly as to literally lift itself up and then down? The noise seems to be rather soft and rubbery rather than metal on metal.
Thanks for your suggestions, guys, please keep them coming!
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replying to passerby, passerby wrote: And so I lifted it again and turned the wheel when the car and the tires were warm. Made no difference - I still cannot hear anything when turning by hand. The noise was definitely there when I was driving it, so it looks like the weight of the car is an important factor.
Would a faulty wheel bearing make the same noise when loaded as when it's not?
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That would be your dampers. How was the tread wear?
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replying to Elmo P. Shagnasty , passerby wrote:

The tires are almost brand new and the thread is still rather deep. So, if there's wear that caused by this issue, it's really hard to see yet.
As far as dampers making the noise: I always thought dampers would make random noises because of the road. And there's no hissing either. Well, as much as I can tell - it's only apparent around 15-20MPH and it's already pretty noisy at that speed.
Do you think it makes sense to have that wheel balanced again for just in case and see what happens?
Thanks!
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That would be the cogging torque of the permanent magnet motor/generators (MG1 and MG2) along with the slop in the PSD, final drive gears, and silent chain.
Remember that the Prius does not actually have a CVT, they just called it an E-CVT because it was the closest category to put it in.
http://prius.ecrostech.com/original/Understanding/PowerTrain.htm
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This isn't it because it wouldn't necessarily be synchronized with the wheel rotation on a 1:1 basis, but a buddy of mine wrestled with a knocking noise that turned out to be a screwdriver left inside his tire.
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replying to Elmo P. Shagnasty , passerby wrote:

Oh, boy! This sounds like one of those horror stories about a surgeon leaving a scalpel inside a patient's body ...
I now think I should definitely take L.F.'s advice and rotate the wheel while suspended and on neutral, all the while keeping your story in mind, too.
When I brought it into the dealership last time, I was mostly concerned about break pads - had a pebble lodge itself in there on a different vehicle that also made weird sounds. They seem to have been going under the same assumption and perhaps didn't look for much else.
As far as the bearing failing, it would seriously suck indeed. I'm so not looking forward to an expensive repair. However, there's one observation that perhaps supports the bearings theory: the knocks seem to become louder when the car is climbing a hill. I can't come up with any explanation for that which would include the wheel. The wheel is round - should make no difference if the car's nose is slightly up.
Thanks!
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Have you had the wheel bearings checked?
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Michael LeVine - snipped-for-privacy@redshift.com
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On 12/13/2012 8:51 AM, Michael N. LeVine wrote:

Brake binding? Interference between rim and brakes or suspension?
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On Tuesday, December 11, 2012 2:08:01 PM UTC-5, passerby wrote:

A possibility that I think has not been mentioned: it's possible that you have a drive shaft joint going. A check for that is to drive in a tight circle for a round or two. Do that in both directions. If a joint is going, the problem will be a lot worse when turning sharply.
(I'd suspect a wheel bearing first, since you have checked the tires. However, worthwhile to check the driveshafts too.)
Larry Van Wormer
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replying to lvw , passerby wrote:

Thank you for the suggestion, Larry. I tried a tight circle and it looks like the knocking sound actually stops while in the circle, then restarts as soon as I straighten the wheels. I did it in both directions, same thing. This mystifies me even more, I have to admit. Still looks like more of a bearings issue than anything else though - as the car shifts, there's perhaps more pressure on a different side of the bearing?
Those driveshafts you've mentioned: interestingly, the one that goes to the wheel I suspect is the source of the noise, is more rusted than the other one. More rust=less oil? I mean, it's on the outside obviously and open to all elements, so there should be some rust (and no oil), but I don't understand why there's a visible difference in amount of rust between the two...
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replying to passerby, passerby wrote:

Turns out, I can post images here after all. So, this is what I meant: this first picture is the driveshaft of the wheel that makes the noise (see the rust where I circled it) - passenger side. click to open the full size version of the image
And the other one (driver side) is much more clean:
click to open the full size version of the image
I don't know if it has any significance at all - I have it scheduled for a dealership visit again next week, will post what they find.
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replying to passerby, Vlad wrote: Any luck figuring out what it was? Were you able to fix it? I am having the same issue now.
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replying to Vlad, passerby wrote: Yeah, I did figure it out. It was the damn tire all along. The dealership was just being difficult and played dumb so they don't have to replace the tire. So I took my business elsewhere. The tire eventually needed replacement anyway. It got replaced and the noise went away.
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