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2008 CTS4 3.6 LY7
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Discussion Starter #1 (Edited)
Has anyone ever noticed a hum noise around 1000-1200 RPM going 35-40 MPH coming from the rear of the car? I seem to hear every once and a while. My 08 has 62200 miles on it......
 
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Did you ever find out what it was? I have a '12 CTS and between 45-60 mph (not sure of RPMs) I get a deep, low hum coming from the rear end. Car has 45,000 mi. I remember doing a test drive a while back and the test car had a similar hum...must be something with this model?
 

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'14 CTS-V LongRoof; '16 ATS-V Sedan,' 04 Trailblazer 4x4; '10 CTS LongRoof gone but never forgotten
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14,161 Posts
Maybe change out the diff fluids. Cheap and easy, and is a good thing to do whether or not it takes care of the situation.
 

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2009 CTS 3.6 LY7
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I'd suspect the diff/fluid too. I have a Chevy van that has a noticeable hum from ex: 45-55 MPH that disappears quickly above that speed. Looking at the shop manual one time I noticed they are actually designed that way i.e. the inevitable harmonics/resonances are designed to occur at less frequent/transitory speeds. There's a whole process/description in the manual about getting the hum speed/tuning right when working on the diff.
 
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