People are loud. If you live in a city where people walk around, you'll hear every conversation from your street-facing windows. Cars are more obnoxious for sure, but they're hardly the exclusive problem contributing to noise.
Stockholm is creepily quiet sometimes. I say this as a New Yorker who needs some kind of background ruckus to sleep.
stayed for a week in Barcelona. there was this little park in front of the hotel where some chirpy homeless people spent the whole night talking. not overly annoying as it was a constant noise.