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2007~2015 Rear Differential Broken?

I have a 2009 mazda CX-9 with 190k miles. Took the car to the mechanic because of a shake at 60+ mph and a hum noise coming from the rear while driving. He said the noise is the rear diff. Is that possible? The CX9 is AWD on-demand right? So doesn't that mean the rear diff isn't even connected during most driving and couldn't be making that constant hum noise.

Both rear wheels have been making a metallic jingling noise over bumps. Maybe the rear wheel bearings are the actual problem?
 
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2009 Mazda CX-9 GT
The rear axle may not be getting power, but it is still spinning/turning while driving, so yes it is possible.

Take it for a second opinion if you don't trust the first one.
 
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2009 CX-9 Touring AWD
I have a 2009 mazda CX-9 with 190k miles. Took the car to the mechanic because of a shake at 60+ mph and a hum noise coming from the rear while driving. He said the noise is the rear diff. Is that possible? The CX9 is AWD on-demand right? So doesn't that mean the rear diff isn't even connected during most driving and couldn't be making that constant hum noise.

Both rear wheels have been making a metallic jingling noise over bumps. Maybe the rear wheel bearings are the actual problem?

I've had all four wheel bearings done, plus the differential mounts.

Post in thread: Anyone else have their wheel bearings replaced?
 
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2014 Ford Explorer Sport, 2009 CX9(Wife's)
I agree with checking wheel bearings first.

My wife's 09 had 2x rear bearings replaced in the 185k miles she had it. Not sure if they were the same one, but I replaced one myself last spring.

I knew what it was right away when driving it.
When I jacked it up, I could spin the rear wheel and feel it grinding.
 
Thanks for all the replies. I took the car to the dealership for a second opinion. They said that the noise isn't the rear diff. That in-fact the rear wheel bearings are the problem.

Unfortunately though they said the splines on the transfer case are bad so I need a new transmission and transfer case. Same old story right.
I don't care about having AWD and the car drives fine. Transmission shifts great. So my question now is can I just keep driving the car like that forever if I don't care about AWD or will it just get worse over time where it does actually effect the drivability and need to be repaired?
 
There are plenty of threads on this but short answer is yes, you can leave it like that and remove the driveshaft for added safety, I personally leave the transfer case out of the car also.
 
I've read through a lot of the threads on this but never found a clear answer if I could just drive the car the way it is since it drives fine. Basically what would happen if I just left it the way it it is? Car drives fine now.
 
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2011 CX-9 GT AWD
I was hearing noise coming from behind the vehicle. I was expecting rear differential. I bought wheel bearings and took it to my mechanic. I told him there is a noise coming from the back. I asked him to replace the bearing, then let's see will it disappear or not. I was lucky and the sound disappeared.

Normally there is a difference between differential and wheel bearing noise but you can not figure out where is it coming from on the CX-9.

If you decide to replace the wheel bearing, you should check the brake dust shield. If they are rusted and you want to replace them, it will be good timing to replace it along with the bearing.
 
Just wanted to follow up with you guys on this.
I appreciate all the advice. The problem was the rear wheel bearings. Replaced both and the car drives great. No more noise or shake.
As far as the transfer case, I don't have any AWD or error codes and the car drives fine. I wonder if the dealer just brings that up on high mileage cars to try and sell you a new car. I wonder if most of these cars transfer cases have gone bad and people just don't realize it until they go to the dealer for something else and the dealer says "ohh you need a new car". Anyways I'm just gonna keep driving it and see how it goes. I'll post back here if there ever is any issue with it... And if there is, I'll just have it removed.
 
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if your transfer case is bad and you don't live in a climate where it is usefull, who cares if it works or not? If it is shot and you didn't realise for over a year than maybe it is because you don't really need it.

Rear wheel bearing tend to go bad on these and they are not easy to change. Good thing you found the probem.