problem with /playsound coordinates

I want to put a sound on a loop to play from a point source using a command block and the playsound command. After toying around with /playsound I came up with a command like the following:

/playsound random.burp @p 45 45 45 1 1 1

While I was within 16 blocks of the source, the noise would correctly sound like it was coming from the specified coordinates. Whenever I moved outside of those coordinates the sound seemed to start coming from my player instead. I was hoping that I could loop the sound and that I would only hear it when I entered the area.

I suppose I can add the /testfor command to check if the player is in range before looping but I was hoping that the sound would simply not play for me when I get out of range.

Can you please take a look at this and see if you can't find a solution/

Thanks