Have noticed this with my car for a while now. Seems to be a whine, maybe almost a howl. It's not very loud; with the radio on or top down, it's nearly impossible to hear. Only occurs during 54-59 mph. Starts right at 54 mph, pitch increases a bit, then by 60 mph it's completely gone. Doesn't happen at any other speed. Only under throttle. Hard to tell if it's just a resonance sound I'm hearing, or if it's something within the diff. I'm leaning towards something in the diff. Changed the fluid out earlier this year. Drained the factory fill, everything looked good, and filled with Amsoil Severe Gear 75W140. Noise didn't change. Car is an 08 with 8,9xx miles.

After some searching through the site, I came across different owners that experienced a similar sound that happened only in a small mph window. Possibly how the gears were set from the factory? Small defect in the gear set or bearings?

 

That seems like awfully heavy fluid for a street car. Same noise before fluid change?

 

The 75W140 is actually a widely preferred fluid, mainly the Severe Gear. It's actually not very thick either, the old LE 90W stuff I've used in the past felt much thicker. Same noise before and after. I might switch it out for some LE1605 and see what happens.

 

Are you really sure it's the dif and not the trans? It seems like your typical transmission whine to me.

 

That's what I have been wondering also. Although, it does sound like it's coming from pretty far back.

 

Mine sings a little at those speeds in the summer months using light throttle in 6th gear. It's not noticeable in winter, other speeds, or other gears. I think it's just a harmonic of the gear set for the parameters mentioned at a specific gear oil viscosity film strength.

 

I agree.I run Amsoil SG 75-110 in my S & Z.

\rlr
Carolina