differential or wheel bearings?

[Spykem4e]

Hi guys,

Since I did the tires rotation on my car, I can hear some sound, like humming sound or a little "zzzzzz" coming from the rear.I just cant tell if its the differential or the tires or one of the rear wheel bearing.

The car is a 2005, Cadillac CTS, automatic with 3.6l with 112k miles on the odometer.

The sounds can be noticeable at:
60-70kph
80kph
115kph-120kph.

between those range or lower than 60, i cant hear a thing.
I cant point if its the tires, differential or wheel hub needs to be change.

I flushed the diff. and put new fluid in it but didn't change a thing. The old fluid was in nice color almost like the new one. I change it every 50k kms.

At 60-65 its more a zzzzzzz just like winter tires.
at 80 and 115 its more like a humming noise.

If its a wheel bearing, since I have the wheel hub assembly with bearings, speed sensor et abs sensor in it, if I try to shake the wheel, will there me some loose if the bearings are bad?

 

[flanso]

Perhaps rotating the tires back to their original positions would tell you if the hum is tire related.

 

[Boomer]

Many years ago, in a 1961 Chevy Impala, I had a noise in the rear end that sounded like a snow tire tread noise. Ran that way for two years; never got worse. Then, one day, it was snowing and I hit a snow filled pothole at 60 mph. The noise stopped! Wow, thought I, problem solved . WRONG! Drove another 15 miles, put on the brakes, and had no brakes! Pulled off, waited in the cold weather for a few minutes, and had brakes again. Started to drive, went around a curve in the road and the whole rear axle came out the passengers side of the car. Turns out it was a bad wheel bearing. Hitting the whole finally did it in. It got really hot and caused the brake fluid to boil. The bearing ate the race, the axle wobbled and the C-clip broke.

Moral: Get the bearing checked!

 

[tomcat27]

I'm thinking wheel bearing. they are easy to check: jack that wheel up (use stands) grab the tire at the top and bottom and try to shake it

 

[Kestas]

That's only for advanced wheel bearing failures. They make noise long before they go into clearance.

 

[tig1]

Tires

 

[mechtech2]

"Since I did the tire rotation".
There you go.

 

[Spykem4e]

update:

Its not tire related. I did the tires rotation + alignment and the sound is still there. I went at a chevy dealer and they told me it could be a wheel bearing issue but since they want to check in the differential first, I didn't let them play in the car just for fun.

I went at a caddy dealer, they said, clearly, you'll need a brand new diff. How much? 1600$ + labor. ouch! Just by curiosity, I left the dealer and I called the exact same dealer but to talk with the service manager and I asked him how much for a brand new diff. for my car: 992$. Is it me or someone wanted to steal me?

Anyway, I went at a specialized transmission diffrential shop and guess what, the owner has the exact same car than mine! He lifted my car, checked it and he ordered one wheel hub. 645$ + labor ouch! It was the cheapest... just to let you know!