You have to be aware that changing the playrate only works in chrome (not FF, like looping).
And also it doesn't sound exactly like changing the frequency of the sample (like it was doable in CC with audio2 I think).
If you have glitches, it's possible that you're playing too many samples on the same channel or w/e and that they are simply distorting, because of the struggling frequencies.
As usual, audio support in html5 is still messy, and I can't wait for FF and chrome to finaly agree on some standard or w/e and finally correct their code in their browsers.
From what I've read on blogs and reports of meetings and other, both companies are aware of the audio issue but in a kind of wait.
I'm not really sure what they are waiting for (rumors that it's being discussed in the wwwc for standardization) and as usual, it's probable microsoft won't follow it.
IE9/10 will still be behind in matter of html5 support, but from all what I've seen, there's more and more dev/mainstream acceptance of chrome and FF as browsers/default browser, so imo, microsoft as more to lose this time, they won't just be able to rely on the fact that IE is the default browser with windows. I'm under the impression that it doesn't really matter anymore and that people won't hesitate do take the leap to have/use another browser to play comfortably html5 games.
Back to the subject, I have downloaded your capx several times, but there are far too many custom plugins that I should install to my liking so I haven't looked into it.