By default, xaudio2 has a limiter active which makes sense but affects the sound being played. Try the following:
1) While only playing this one sound, switch off the limiter and see if it still crackles.
2) Open your wav-file with some sound editor and select the first milliseconds (ca 25-50 ms should suffice). Then use a fade-in on that part. Save it and try again with and without the limiter. Does it still crackle?
------------------------------------------------------------------------
I had the same problem. Solved it using tulamides example:
I removed first couple of spikes. (everything before the red line)
<img src="http://dl.dropbox.com/u/22173473/sounderror.png">
Also make sure your sound doesn't overlap on loop.