I've uploaded a small demo based on the shade-c examples showing the problem:
http://www.mediafire.com/file/v3bktj65kwn8pld/sound_test.zipYou can move the player with wasd and mouse and play sound with e key.
On my computer on the origin position the sound plays fine, however if I move the player the volume gets lower like if the sound is still played at the origin position.