The Stages Bike uses an enclosed belt-drive system, which produces almost no noise. Expect around 50-55 dB of ambient noise while you are riding the bike.
The electronic braking system on the bike makes a high-pitched noise as more resistance is applied. This noise is normal and is relative to the resistance applied to the bike, i.e. the more braking applied to the flywheel, the more obvious the sound. If you are particularly sensitive to high-pitched sounds, you may want to consider wearing hearing protection to block out this sound.