FireItUp: One other thing it could be is the tempo stretching settings. If you render the song to WAV, select the option for "Render Using Highest Quality Tempo Stretching" then play the exported WAV file and see if you can hear the swirling again. You can also click the Gear icon in the mixer and set the Tempo/Pitch Stretching Quality to High, though this will use more CPU power while playing back.

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