When your Google Nest speaker or display recognises the hotword ('Ok Google' or 'Hey Google'), it records what you say and sends the recording to Google to fulfil your request.
To get a brief sound at the start and/or end of your request:
- Make sure that your mobile device or tablet is connected to the same Wi-Fi network or linked to the same account as your speaker or display.
- Open the Google Home app
.
- Tap Favourites
or Devices
..
- Tap and hold your device's tile.
- Tap Settings
Accessibility.
- To get a sound after you say 'Hey Google', turn on Play start sound.
- To get a sound after Google Assistant stops listening, turn on Play end sound.
.
or Devices 
..
Accessibility.