Heavy “screaming” at start-up

Hello, I drive a V70 II, 2.0 Turbo, year 2002, 179 HP, petrol. For a few weeks now, my car has been giving a loud noise when starting, and especially when it’s cold. It sounds like something is going on somewhere. Similar to a loud howl. It’s also striking that it appears more often when driving backwards, so out of the parking space. Can someone give me a tip? Would you be very grateful! Achim