array_rand

        <?php
        $files = glob("http://domain.com/dir/*.mp3");
        $random = array_rand($files, 2);
        $files = $files[$random[0]];
        $files = $files[$random[1]];
        ?>
        <!-- <audio controls="controls">
        <source src="<?php echo $fname1; ?>" type="audio/mpeg">
        </audio> -->
        <object>
            <param name="autostart" value="true">
            <param name="src" value="http://link.com/">
            <param name="autoplay" value="true">
            <param name="controller" value="true">
            <embed src="<?php echo $files; ?>" volume="30" hidden="true" controller="true" autoplay="true" autostart="true" type="audio/wav" loop="false"/>
        </object>