I think I have something similar in my 7.5. Last week when it was very hot and my car had been sitting out all day in the sun I noticed a faint whirring noise behind the dash, after the AC had been on full for some time it slowed down but then picked up after I had parked up and switched off. I was worried that something wasn't right as it also sounded like something was hitting the fan (card in spinning bike spokes).
Since the weather has cooled off a bit the noise has gone, it makes sense that there would be a fan just for the Infotainment system.