If you can still drive the car, have someone sit in the back seat and see if the noise is in the rear or the front.
When my rear diff went, I swore the whine was coming from the tranny. The noise travels up the driveshaft to the tranny.
I pulled the tranny and had it opened up to find nothing wrong that would cause that noise. My buddy said pull the rear diff, it must be bad.
213,000miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.
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