Funny swooshing noise....

I have a 2016 Prius with about 40K miles on it. Particularly when I leave for work in the morning, it makes a soft ticking or clicking or swooshing sound that varies with the speed of the car. It's most noticeable between about 10 and 20 or 25 mph. Today, I drove the car after it had been sitting for a week, and the noise was particularly loud - but it pretty much disappeared after I'd driven 7 or 8 miles. It's not just when I'm braking or turning. I think it's coming from the front of the car but I can't be certain. Any thoughts? I'm pretty much an automotive moron who can't do anything more complicated than changing wiper blades, so suggestions would be greatly appreciated.