If you are using a YubiKey NEO on Windows, you may experience Windows playing the USB disconnect/reconnect notification sounds when tapping the capacitive touch sensor to generate an OTP. This is caused by the YubiKey NEO disconnecting and reconnecting the smart card so that it can switch to the OTP mode to generate the OTP. If you want to prevent this, you can disable CCID mode with Yubico Authenticator, if you don't use PIV, OATH, or OpenPGP, or you can disable the notification sound in the Windows settings (preferred). Alternatively, consider upgrading to a newer YubiKey model that supports additional applications and offers an improved user experience.