There is a new paper in the Geophysical Research Letters that may explain why these sounds are happening. The different sizes of the sand dunes can shape the sounds that the san dunes make. Researches have studied the sand in Morocco and comparing sample from other various sand dunes. The different sand dunes of course made different sounds, some made a G-sharp (105 Hz) and others which oscillated between F-sharp and D (90 Hz to 150 Hz). The form of the sand grains was the main reason the sand dunes made different sounds. Here’s a video that shows the san dunes singing:
