Vibration xperia x

[GoldLenor]

Translation via Google Translate:

After the last update, it periodically vibrates without notifications.

После последнего обновления периодически вибрирует без уведомлений. 

[Strampke]

Maybe you have set notification by vibration on in one app.

This app warns you with vibration.

Try to find if your mail, WhatsApp, fb or any other app has a message after you notice a vibration.