Freelander 2 (LR2) Slight whine on deceleration?

Hi,
Just bought a 2007 Freelander 2, 85,000 miles. I find, (now that my ear has become accustomed to the sounds in the cabin), that there is a definite whine on the over-run or as I back off the throttle, that vanishes under load. It's a fairly low level sound, certainly doesn't sound like something in imminent danger of failure. Coasting in neutral doesn't alter the sound, but any acceleration stops it.

Any ideas where I should look guys, or should I just turn up the radio? Is this likely to be heralding the dreaded diff failure and is there any way to check?

Thanks in advance for your comments.

Sound on over-run is normally down to gears, slightly out of mesh. However it could be down to oil that's past it's best.

I'd replace all the fluids in the drive train, then see if it's made a difference.

The daughter has a Citroen c3, which whines in 5th on over-run. On that it's a sign the gearbox is past it's best, but it'll outlast the car, so it's going to stay whining.