Rear end humming noise

[olliesshop]

I have an AWD 2006 Vibe with 89,000 miles and the last few months it's had a humming noise coming from the rear. I notice it most around 30 mph. Also, it doesn't seem to change pitch with vehicle speed.

Based on my reading, mainly on this site, it looks like it could be the following:
• Viscous coupling bearings ... I just replaced the bearings and it didn't eliminate the noise.
• Rear differential bearings ... I hope it's not this, since I've changed the fluid per the maintenance schedule.
• Rear wheel hubs/bearings ... The noise doesn't change when I turn left or right, that I've noticed. Although, I haven't tried any really hard turns.
• Rear axle / CV joints

I'm going to put the rear up on stands soon and check if there's any play or noise in the hubs.

Any help would be greatly appreciated.

Thanks!

[jolt]

a humming noise coming from the rear. I notice it most around 30 mph. Also, it doesn't seem to change pitch with vehicle speed.

Pitch should change with speed and load changes on the rear drive train. I wonder if it is something from the fuel tank, or a shield under the car vibrating at that speed. Check your shields under the car and on the exhaust system. Bend them to try and stiffen them.

[olliesshop]

Pitch should change with speed and load changes on the rear drive train. I wonder if it is something from the fuel tank, or a shield under the car vibrating at that speed. Check your shields under the car and on the exhaust system. Bend them to try and stiffen them.

Thanks! I checked the shields and the exhaust system and they all seem solid.

Also, I need to clarify the noise. It's pretty low-pitched vs. a sheet metal noise. Also, the more I think about it, it does change with speed. There is no noise standing still and it gets louder proportional to speed to the point the other noises mostly drown it out. I can still hear it on the highway, but I have to listen carefully. To me it sounds like a bearing somewhere. But I really don't know.

I hope we come up with a relatively inexpensive solution, but I'm not counting on it.

Thanks again

[thebarber]

Recently rotate the tires?

[olliesshop]

Recently rotate the tires?

Nope, but that's a great idea. I'll rotate them today and see if the noise changes.

Thanks!

[olliesshop]

Update - I rotated the tires and didn't notice any change in the noise. On the test drive I did confirm the noise changes pitch with speed, from a very low pitch at about 15 mph to a slightly higher pitch at 35-40 mph. I also tried to test if it made more noise when turning and I couldn't tell any difference. What I really should do is put it up on stands and get underneath with a stethoscope, but I'm I'm a little scared about doing that, frankly. Maybe I could have the Dealer do that and see what they come up with. Hopefully, though, we can come up with answer without taking it somewhere.

We'll see.

[ehoff121]

Based on my reading, mainly on this site, it looks like it could be the following:
• Viscous coupling bearings ... I just replaced the bearings and it didn't eliminate the noise.

Does this mean you replaced the two bearings inside the rear differential?

http://workshop-manuals.com/toyota/matr ... ng_noises/

[jolt]

I believe this is the service bulletin that ehoff121 is referring to:

http://www.toyotaparts.metro-toyota.com ... 002-07.pdf

This one has more detailed info for the dealership from Toyota.

[olliesshop]

Sorry for the late reply ... BTW, that's is the right service bulletin. I removed the Viscous Coupling & housing from the front of the differential and replaced the front and back bearings. One of the bearings was a little tight, but it turns out that wasn't causing the noise, since it's still there.

I then had my brother drive around the neighborhood with me in the back with my ear to the rear floor. The sound was coming from the center, right over the differential. So my current plan is to buy a new Differential Assembly and replace the current one. The cost for a new Matrix differential is $851 from a Toyota Dealer. I'm also hoping to get a couple hundred for the old differential, so the net cost will hopefully be under $700 ... we'll see.

Thanks!