The fact you don't see references to this in the forums is indicative of the fact that (at least for me) this is the first such report I've seen of this specific behavior. It could be that it's a bug. Following that, I'd strongly urge you to file a bug report on it using the link below:
The behavior you are describing is consistent with what I might expect of the Background Audio and Slide narration.
If you aren't using Background Audio, perhaps try clicking Audio > Import to > Background so you get the dialog. Then configure the dialog so you clear the option for reducing the volume.
Once you have done this and clicked Save, click Audio > Remove > Background and see if that fixes anything. If not...
Try clearing the preferences and publish again,
My crystal ball is on the fritz and my psychic skills are nearly non-existent, so I can't tell whether you are using the Mac or the PC version. But if it's the PC version, here is how you clear the preferences.
Right-click the Shortcut icon and choose Properties
From the Shortcut tab, click the Open File Location button
Windows Explorer should open - From there, locate the Utils folder
Double-click the CleanPreferencesWin.bat file
Restart Captivate and test
While we're on this subject, is it possible to disable the mouse click sounds when you're recording? For me, they seem to be as loud as my voice.