Whining Noise - Diff/Trans?!

Moved from Main Discussion - in the hope of getting a response.

Dear all,
Over the last few weeks my car (840 ci) has developed a whining noise coming from the front of the car. It is only noticeable on deceleration (not braking) and slow acceleration. It is noticeable when driving in straight lines.
It is an automatic, gear changes are fine with no clunking or hesitation and no messages on the OBD.
I had the transmission and differential oil changed about 20 months ago at Phoenix. Prior to that there was a small leak, I think it is still there, but not much more than previous. I had a new stereo fitted 10 months ago and the engine and check engine lights have not come on since when starting the car (I was told it was most likley the bulbs but have not had time to check).
I would like to take it on a long journey but a bit reluctant to as I do not want to take any chances.
Any thoughts would be much appreciated.

Dear Timm,

Thanks for getting back to me.
I took the car for a drive last night and noticed the noise is heard loudest between 20-40mph, after which it almost disappears, it is also louder with the windows down. When decelerating from higher speeds, the noise kicks in at about 50mph and is noticeable down to 20mph.
I have noticed it is even louder when turning the streering wheel a few degrees to the left (if I turn the steering wheel back to neutral it lessens and then disappears if I turn it a few degrees to the right), it seems to be coming from the bonnet or the front of the car. I can only describing the noise as a whining/creaking sound, likle something rubbing against something else.
Other than that the car drives fine, accelerates and brakes as normal, no OBD bongs/messages, and the ASC light flashed as normal last night.
Your thoughts would be much appreciated.

Thanks Smileitsme,
I have booked the car into Phoenix Motorsports so Gerry can have a look, I wanted to take it for a long drive over this coming weekend so don't want to take any chances, will keep you posted on the outcome.