Sure, I'd love to nail down the cause and help fix it.
I've deleted the folder, then reinstalled Jetpack, and connected it to Wordpress.com.
The post with the post format of audio with an MP3 works fine still:
http://nickmarlbroughauthor.com/i-dare/
The page with an MP3 file embedded now no longer works:
http://nickmarlbroughauthor.com/audio-test/
Here's the error log output
root@vps1 logs]# tail /hsphere/local/home/wwwuse0/logs/nickmarlbroughauthor.com/error_log
[Mon Jan 13 12:37:12 2014] [error] [client 192.80.3.219] (104)Connection reset by peer: FastCGI: comm with server "/hsphere/shared/php53/bin/php" aborted: read failed, referer: http://nickmarlbroughauthor.com/wp-admin/edit.php?post_type=page
[Mon Jan 13 12:37:12 2014] [error] [client 192.80.3.219] FastCGI: incomplete headers (0 bytes) received from server "/hsphere/shared/php53/bin/php", referer: http://nickmarlbroughauthor.com/wp-admin/edit.php?post_type=page
If visited using an incognito window:
[Mon Jan 13 12:40:26 2014] [error] [client 192.80.3.219] (104)Connection reset by peer: FastCGI: comm with server "/hsphere/shared/php53/bin/php" aborted: read failed
[Mon Jan 13 12:40:26 2014] [error] [client 192.80.3.219] FastCGI: incomplete headers (0 bytes) received from server "/hsphere/shared/php53/bin/php"
That's all I see.
If I deactivate Jetpack's shortcodes completely, it still happens. If I deactivate the plugin, it works again.
Ah, if I switch to FastCGI on PHP 5.2, it works ok. If using FastCGI on PHP v5.3, it errors out. It's only a problem on v5.3.