HU, the sound of all sounds
"The sound of HU is the source of all sound, and sound is as close to the source of life as we can get. Any living being can experience sound first hand by vocally participating in it, but we can only experience light by being exposed to it. That is because we can make a sound with our vocal cords, but we can not make a light with any organ of our physical body." (From the http://lovinghu.blogspot.com blog)

"Singing HU draws us closer in our state of consciousness to the Divine Being. This is its purpose. It is for those who desire spiritual love, freedom, wisdom, and truth." (From the http://www.eckankar.org web site)

From the Official ECKANKAR YouTube site:

Experience the Light and Sound of God 

Discovering Who You Really Are - Soul

Insights into Soul Travel and Astral Projection

Ways of Spiritual Dreaming

Play HU sound (click here). 1:25 min, 64 kbps. Size: 0.667 MB

Or click on http://www.eckankar.org/hu.html where you can find two 5-minute HU songs to listen to at 4 and 11.7 MB.