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Discussion Starter #1
I'm hearing a hum from my rear (not me the car, this time :lol: ) It started a couple of weeks ago. It's relative to the speed of the car and not the engine so I think it's between the transaxle and the ground, most likely a bearing. It was time for my service so I asked the local Toyota service to listen to it and have a look. After trying to push other various "services" on me they said the rotated the tires and the sound was gone.

I drive away and it sounds the same. I'm sure they didn't know what to listen for or never drove it.

Anyone here with rear bearings going out? What were the symptoms. I would think it would sound different when you turn, putting stress on one side or the other. Are they fairly easy to replace?
 

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Jack up the car, one side at a time, and manually rotate the rear wheels. If it's a bearing you should hear something. If it's a brake drag, you should feel the resistance when rotating the wheels. Are you sure you are not hearing the fan for the traction battery?
 

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Discussion Starter #3
It wouldn't be the fan since it's directly related to the speed of the car. It almost sounds like the car has mud grip tires, only faintly. The sound is most prominent as speeds between 40 and 55 and I can only hear it when the road surface is smooth and quiet. I don't feel any vibration. My milage has suffered though. I'm only getting 42 when just before my batteries were replaced I was getting 48-50 (but that's another story).

I'm gonna jack it up as soon as I can and see if I notice anything.
 

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I wonder if it could be brake dust buildup. I used to get a noise from the brake shoe dragging in hardened built up brake dust. In my case, it was noticeable at low speed. The dealer cleaned and serviced the rear brakes and that took care of it. There are posters here who disagree with the need for servicing/cleaning brakes, and call it gouging by the dealer. Mine includes it with tire rotation, so I have them perform that service at 10K intervals, and I do just a rotation in between.
 

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Discussion Starter #5
Last night I jacked up one rear wheel at a time, just barely clearing the floor. I spun the wheel and didn't notice any noise or dragging. BUT I did hear the tire brushing in one spot and I could see it was about .125" out of round. I looked to the other side and got the same thing but not quite as out.

I took it to the place i got the tires they didn't see anything wrong and did a cross rotation and suggested it may "go away" in time. We'll see.
 

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Wow. I feel angry for you just sitting behind the computer hearing that the technicians didn't do anything fix the humming. So often, you will tell these guys something and they will just outright ignore you and tell you that they fixed it. I once was told by a tire shop that "nothing was wrong with my tire" when they hadn't even looked at it. It was flat, and they said "it's supposed to look that way", and when I said I'm pretty sure it's flat -- then he admitted he hadn't even looked at it and then upon inspection, agreed that it was flat looking.

Find a reputable shop/dealership that you can trust to do the work they say they're going to do, because there are a bunch of swindlers and lazy people out there.
 

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Discussion Starter #7
Well I've had a while to drive it and the hum is still there. It's not changing when I turn hard so I suspect it's the CV's. I WON'T be taking it back to Toyota!!!
 

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What year of Prius do you have, and what is the brand, model and size tire on your car? Also, where are you located? 42 mpg isn't unusual if you are in a snow state, as mileage usually goes down when either the heater or air conditioner are running. Snow is especially bad, because besides the ICE running longer to heat hot water to keep you comfortable, you may also have some slippage in the drive train due to snow and ice.

Do you have a friend or relative that has a Prius that you could swap the rear wheels to see if the sound is still there?
 

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Discussion Starter #9
I live in Atlanta, no snow. The tires are Falken, not sure the specs. But they are the correct size and load range for the car. I was getting 49 mpg a year ago :cry: .
 

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Not sure anyone can help you much with the humming, since one would probably have to ride in your car to figure out exactly where it is coming from.

In any case, just a couple of comments on previous posts in this thread:

* Regarding the humming sound: I have heard an electronic humming coming from the hybrid electronics at around 40-45 mph. It is only noticeable when the weather is nice and I'm driving with the windows down. I suspect that this sound is always present, but only noticeable under the right conditions. If that is what you hear, there probably isn't anything you can do about it other than roll the windows up and turn on the blower for the heater or air conditioner.

The humming could also come from the tread design of your tires. Do you have snow tires or ones with large/deep aggressive sipes? Again, I'd recommend trading wheels and tires with another Prius for a test drive.

* Regarding poor fuel economy: Do you track your mileage with every fillup? What mileage were you getting during the same period last year? Mileage is really affected by tire pressure, driving style and outside temperature (which affects heater and air conditioner use). I have Michelin HydroEdge tires rated at 44 psi and keep them inflated to 44/42. My daily commute is on city surface streets at 40-45 mph, with synchronized traffic lights. Fuel economy is highest at 51-53 mpg in the spring and fall when I drive with the windows down without the heater or air conditioner running. It is the lowest at 44-46 mpg in the summer and winter when both are running most of the time. Also, I drive almost exclusively with the cruise control on to maximize the percentage of time that the hybrid system is controlling acceleration, cruising and braking, and I use the throttle and brakes only during full-throttle starts from every traffic light and the brakes only during the last few feet of slowing. And, I try to time the synchronized traffic lights so I do not stop at intersections. This sounds counter-intuitive, but this technique has proven itself to be the most efficient over the years.
 

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Discussion Starter #11
I've been driving this car since the Summer of 2000 with 217k on the clock. Until the past year I never put more than 34 lb in the tires. And the tires I bought before then were not ever rated for the proper load range, the local shop fitted the proper size and didn't acknowledge the Prius tire specs. I've averaged 47-50 all these years. I am aware of the changes in mileage according to the seasons. The mileage drop pretty much happened soon after the hybrid battery change a year ago. Unfortunately, I got new tires a week after the battery so I can't pin point exactly when it happened. The didn't start until a month ago.

If the sound was coming from the tires it would be a much higher pitch OR I would feel it.

Maybe I'll get enough of a bonus or Christmas money to have it checked out after the holidays.
 

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Did you ever figure out what the noise was?

I have a 2002 Prius with 170,000+ miles. The batteries were replaced last summer.

For the past couple months I have had a humming coming from the rear of the car. It seems to be getting progressively louder. Before the batteries were replaced I had one of the rear wheel bearings replaced. The hum sounds very similar to the hum when the wheel bearing was going out. However, when I recently took it in to the dealer they said my wheel bearings were fine and told me it was probably the tires. I have since had the tires replaced and the hum continues.
 

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Discussion Starter #13
No, I haven't found the noise yet. I'm thinking it's the bearings or CV's but wouldn't it make a different sound when turning. Especially the CV's I thought would make a clanking noise while turning.

I was told that it was probably the tire at the dealer service. They said they rotated and the sound went away. They were wrong. They never drove it before hand and never knew what to listen for. The sound is most prominent at 45-55 mph.

If your like me and have driven this quiet car for 10 years you're acutely aware of any new sound it makes. My mileage has dropped from 49 to 43 in the past year.
 

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It's not CVs if the sound is coming from the rear. No CVs back there.
Probably a rear wheel bearing. No harm in waiting for it to get a little worse so you can be sure.
 

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Discussion Starter #15
I'm seeing some talk of $400 per side for rear wheel bearing replacement!! Looks like the bearing are not "user replaceable" and the hub/bearing comes as a big expensive unit.

Has anyone here ever replaced them at home?
 

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So I have been looking around to figure out the humming and found this thread. I have the humming as described and varies with speed. Was the rear bearing replacement the resolution?

2010 Prius 129k
 
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