I cleaned up the epub and attached the mobi. I am doubting that classic problem is the issue in regards to Kindle. They have their own requirements that don't always follow epub standards.
Withing the audio tag you can find how Kindle directs us to embedd sound. Kindlegen will complain if it can not find the audio. It is not doing that anymore. The only remaining thing not validating is this official way to put embedded audio as directed by Amazon. I am guessing it's not meant to. Can somebody try the mobi on their Kindle HD or 2 gen Fire please?
<div id="audiodiv" class="Basic-Text-Frame">
<audio id="audio1" src="audiovideo/myzuka.mp3" controls title="This is my audio
(1:10)">
<br/><br/><br/>
”There is audio content at this location that is not currently supported for your
device. The caption for this content is displayed below.”
<br/><br/><br/>
</audio>
<strong>This is my audio (1:10)</strong> </div>