Decided to get measurements with the service loaner Model S vs my Model 3, for those who care. The Model S had a whopping 108 miles more than my 3 when I turned it back in compared to when I got home.
All measurements taken using "Decibel X" version 6.1.0 on iPhone X running iOS 11.2.5
Moving samples were captured on the same general stretch of road, with the phone directly in front of the steering wheel airbag but not touching.
The idle measurements are taken in my office parking lot with minimal nearby traffic, but not completely silent. I didn't think to capture the S in my garage with the door closed, which would have been ideal.
Model S - December 2017 build, 19" wheels:
0mph, fan off, 30 seconds: avg 49.6dB, max 51.8dB
0mph, fan set to 3, 30 seconds: avg 68.4dB, max 68.6dB
65mph, fan off, on smooth surface, 10 seconds: avg 84.0dB, max 87.4dB
Model 3 - January 2017 build, 18" wheels:
0mph, fan off, 30 seconds: avg 51.2dB, max 52.6dB
0mph, fan set to 3, 30 seconds: avg 56.9dB, 58.5dB
65mph, fan off, on smooth surface, 10 seconds: avg 82.8dB, max 85.0dB