Hi mate
How did you go with the gearbox whine?
I have a 08 omega 4spd 3.6, & does the same thing! The whine (which is similar to a diff noise - best way to describe it & no its not the diff), starts also around 50kmh through to 60kmh approx.
It's not tyre noise, Diff, wheel bearings etc.
Did yours do it in any (forward) gear & neuatral & appear to be more noticeable cold & less noticeable warm?
Cheers obei:idea3: