Auto transmission noise problem 1990 535

[Gary535]

I’ve noticed over the last few weeks that there is a loud whirring/ humming noise coming from the auto transmission. This only happens after the gearbox is warm- say after 10 miles and is mostly noticeable coming from 1st and 2nd gear. There is no noise when I first drive off and the car is cold. The transmission engages and selects perfectly.

My worry however, is that the transmission is overheating and the noise could be a sign of trouble to come or burnt ATF etc. At the same time, I don’t want to have the tranny inspected/ serviced if it’s a common symptom and nothing to worry about.

Could there be a problem with the cooling system?

Any advice much appreciated!

(1990 535 90,000 miles)

[wingman]

This sounds silly but was the A/C on? I'm not talking about air noise but I'll get compressor noise which sounds like the tranny but only when the A/C is on cold. Strange but true!

[Gary535]

No- i actually first thought that it may have been the radiator fan, but i checked and the noise if definatley from the gearbox.
Could excess temperature cause the oil to thin or temporaraly change viscosity?