Slashes removed from source URL

I created a tool tip with the title “audio test” like this:

<audio controls=”controls”>
<source=”https://example.com/wp-content/uploads/2021/02/mpthreetest.mp3&#8243; type=”audio/mpeg”>
Your browser does not support the audio element
</audio>

When I mouse over “audio test” in my page, the audio control pop-up appears, but when I inspect the code I see that all the slashes have been removed from the source URL. I have tried doubling up on slashes, or using \/ but the slashes always get removed.

Any suggestions?

Thanks,

steve