Please could someone help I have just bought an A5 Quattro 2008 3.0tdi 110 thousand miles has a whine from the gearbox in All gears doesn't fluctuate just a constant noise drives perfect gears easily change clutch is light as expected would an oil change help 

Is it gearbox or diff? 

Almost certain noises from gearbox six speed manual 

If it's been bought from a dealer within the last 30 days then the dealer has the responsibility to fix it FOC or take the car back for a full refund. 

No unfortunately a private purchase now not sure if it's coming from the gearbox or diff . thanks everyone for your help 

Thanks Ian, 

Please come back when you believe you have narrowed it down to a more specific location. 
Differential noise can usually be made to alter by assessing whether the noise changes on smooth acceleration and decelerating. 
Kind regards,

Gareth. 
p.s. please do not assume that a private purchase results in no comebacks. The vehicle must still be as described. That is why sellers now simply state ‘ Starts, stops, drives.’

Thank you very much for your help