FL1 TD4 Auto - Transmission whine after cold start

This afternoon a great Sage assisted me with this ongoing auto box issue. My suspiscions were that fluid levels may be playing a part in the whine that is occuring. We discovered that the box was overfilled by approx 1L. Hurrah I thought. All will be well! Sadly though, after the level was corrected the whine is now ever present under acceleration/load. I think as a result of today we've narrowed down the problem to the auto box, and probably not the IRD (although both are obviously high mileage) but further investigation is needed, and probably by an autobox specialist. The excess fluid (replaced in february) did appear to have some contaminant/burnt element to it but can't be sure.