I had a similar noise issue but was convinced it was a whine coming from the torque converter. After only managing to top up about 125mls gearbox fluid I found the noise was still present. Turning the AC to ECON the noise went away. Transpires that although the noise was more distinguishable in the cabin it was the AC compressor (low on coolant). AC guy did say though it's probably time to plan for a new compressor as the bearings could also be on thier way out.
These cars never stay fixed
