Retrieve commented value from xml file in PHP

This is my XML file;

<?xml version="1.0" encoding="utf-8"?>
<rss version="2.0" xmlns:media="http://search.yahoo.com/mrss/">

<serial>PQE43A021640</serial>   <!--    3693    -->
<serial>PQE43E015072</serial>   <!--    3694    -->
<serial>PQE430015069</serial>   <!--    3695    -->
</rss>

In above xml file has commented values next to serial node.

I have got serial number using this script

$xml=simplexml_load_file("note.xml");
foreach($xml as $val) { echo $val[0] . "<br>"; }

So how can I get that commented values next to serial number? And also I just want to get that particular line number? those 3 should same line values : e.g (line num : 4 | serial num : PQE430015069 | comented num : 3693 )

Please help,