Visible speakers in the walls
All speakers look the same. Put on your headphones and explore the places on the map where the sounds come from. In some places you cannot see the speakers, so ignore these sounds.
There are 13 speakers in the Warcraft zone.
There are 12 speakers in the Starcraft zone (you need a good speed boost to get two of them). The other two speakers in this zone don't make any sounds.
There are only 3 speakers in the Diablo zone (in front of the castle, including the gate).
Jump on nearby objects to reach some of this speakers