I've been a big fan of PowerPoint and iSpring Free lately, so it kind of figures I'd have a problem with both! I found a professor's iSpring Free tutorial did not include audio and the speaker indicating PowerPoint audio was still visible in the published version. I tried it myself and - sure enough - same issue.
To fix it, we had to click on the speaker icon on each slide and new tabs come up with options. The default is apparently for the audio to start on click but it needs to be changed to automatically. Also, the "Hide During Show" box needs to be clicked for the speaker to go away.
Unfortunately, it doesn't seem to retain these properties from slide to slide, so you have to change these options for every slide with audio. Four extra clicks per slide. Not cool.
In addition, PowerPoint audio is just not very good. It sounds like it picks up a lot of background noise. It's not my mic though; it is fine in Camtasia and Screencast-o-matic. These factors are causing me to reevaluate my recommendation of iSpring Free, unless I can figure out how to make the options stay.
Here's a screenshot of the Playback tab with the correct options. I'm having trouble making it a decent size for the blog, so click on it for a larger version.