It is proper Netiquette to use a silent tone setting to prevent noise. Don’t think vibrate is silent.
Ringer Netiquette Smartphones
Turn your smartphone off completely or to silent in meetings or other places that they are banned to avoid unintended interruptions.
Vibrating phones make noise. Sometimes a vibrating smartphone is louder than a ringtone. Large smartphones on the vibrate setting cause a very loud rattle when they vibrate on hard surfaces.
Vibrating phones in pockets can be amplified by metal pens and the other contents of pockets. There are many things that can cause a vibrating phone to be a audible distraction.
Vibrate is not silent because it makes noise when it vibrates against something.