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I have a 2004 Volvo S80 2.9 with 79,000 miles. Traction control (STC) is installed.<p>Recently a low pitched hum (or groan when first starting from a complete stop) has emerged from what I believe to be the front and center portion of the car. The hum/groan does not synchronize with the revolution of the wheels (with the car's speed). I've asked a passenger to try to identify the direction of the sound's source, and that passenger believes it to be coming from under the floor board, closer to the driver's side. Once I travel faster than 30 MPH, the hum fades away, but sometimes it recurs intermittently, especially when I'm on a highway and I turn the the wheel in either direction to follow a curve in the road.<p>Based on the details above, I fear that the hum is coming from the differential, or the transmission if the differential is not a separate unit on the front. Could anyone tell me how to diagnose and confirm a failing differential when the vehicle is stationary and up on a jack/lift/ramps? How do I rule out that it is not a bad wheel bearing or a bad CV driveaxle that is making the noise?<p>If the culprit is a failing differential, can it be separated from the transmission in the front, and is my only repair option to have the differential replaced ($$thousands!)?<p>I'm grateful for your information. Thank you.<BR><BR>
<i>Modified by zealousagenda at 6:57 AM 5-14-2009</i>
 

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Re: Hum at slow speed from differential, CV driveaxle, or bearing? (zealousagenda)

Probably a wheel bearing
 
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