XC60, D3,Geartronic’s whimpering, rattling, whistling noise at the cold engine?

Hello and good morning in the round. Yesterday, where I drove home from the service (- cold engine) and had my side window on (- along a house wall and up mountain, therefore just there to hear well…) I noticed it – a erring, rattling, whistling noise, somehow under the car???? After about 2 km the whole haunting was over… It is interesting that this noise is just under load, so when giving gas is especially good to hear …. Is it good morning? I’m sorry, if someone might seem like a banal question, but that’s my first car with an automatic transmission (- fully enthusiastic!) and just yesterday I noticed it for the first time, because I happened to have the window on when I started, which actually doesn’t happen so often in the winter. As soon as I did the window again, there was nothing to hear… I’m really insecure now… Maybe someone can help me and tell me what there is (-Bj. 08/2016, D3, Geartronic, just run 38500 km…) Greetings and good ride to all of us here! – Jacek