All electric scooters make an electric almost humming sound when operating. They tend to get louder when going faster.
We haven’t ever tested noise levels, but I’d that none are very loud – definitely much quieter than a car or any other gas-operated vehicle.
Generally smaller less powerful scooters are quieter than larger dual-motor ones, but no scooter is particularly loud.
A handful of scooters are chain-driven but most have hub motors. I suspect the chain-driven ones are louder because of that mechanism, but we’ve never tested one.