A whine in neutral or Park indicates a failing pump or pump issue. A whine in gear indicates a failing torque converter. It sounds like the forward pump is failing in your case. Has the fluid ever been changed, or even had it's level checked, in your transmission?

 

A cold-start whine can also be caused by the power steering pump, the alternator, or any of the serpentine belt idler pulleys.

Remove the serpentine belt when the engine is cold, and then start the engine. If the whine is still there, then you've isolated it to the engine or transmission.

If the whine disappeared, replace the serpentine belt, restart the engine, and use a mechanic's stethoscope ()or a 2' long piece of 3/8" wooden dowel) and probe PS pump, alternator, AC compressor, etc. to determine exactly where the whine originates.

 

I agree on the noise location search to narrow down the exact location. But he said the noise disappears when shifting into gear. Since he has 177k on the transmission, it would be good to know if the fluid has ever been changed.

 

At a cold start, the engine will be running at high idle speed, (maybe 1,200 to 1.500 RPM).

Shifting into gear will immediately drop that to ~600 RPM, so you really don't know if any change in whine is do to the transmission being in gear, or simply to the change in engine RPM.

I'd also take the cap off the power steering reservoir and see if there is any fluid aeration during the 'whining'. Moisture-contaminated fluid in either the PS system or the transmission can cause cavitation and whining.

The torque converter in the A750 series transmissions is pretty bullet-proof, a hard mechanical failure in the TC itself is rare.

Knowing when the transmission fluid was last serviced would be useful.

 

Alternator maybe

 

One would assume his mechanic knew how to search for a drive train noise. But then again, maybe not.