Create the sound map

Save your work
In Resource Browser, do a search for AmbientSounds_Everon.et or AmbientSounds_Arland.et
Drag one of them into the main preview window
In Resource Browser, do a search for SoundWorld_Base
Drag it into the main preview window
Select the Export Map data tool
Click the .. button next to Destination Path
Select your Terrain folder
Next to Type, select Soundmap
Press Export
Select the SoundWorld_Base entity
In Object Properties, go to where it says Soundmap and press the .. button next to it
Locate and select your soundmap (terrainName.smap)
You might need to restart the entire workbench to start hearing it