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Oh, I had the same problem a while ago.
To fix it, you should go to Publish Settings, which is under File. Once you click that, a dialogue box will open. In the dialogue box there are 3 tabs that read Formats, Flash and HTML. Go to Flash. Now you'll see a bunch of settings, go down to Audio Stream and Audio Event. Click Set for Audio Stream. Another dialogue box will open and in here you change the Bit rate to 160 kbps, uncheck the box that reads, "Convert Stereo to Mono" and then set the quality to Best. Now do the same for Audio Event. Click Publish, and then OK.
Hope this helps! Your audio should become much clearer.