Weird numbers with trackback_url()

Hello,
In my comments.php i have some VERY simple code which is giving me some weird output, here is the code:

<h3 class="comments_headers"><?php comments_number('0 responses', '1 response', '% responses' );?> so far &darr; (<a href="#comment_frm">Write yours</a> or <?php if ( pings_open() ) : ?>
31 	    <a href="<?php trackback_url() ?>">Trackback<?php // _e('TrackBack <abbr title="Universal Resource Locator">URL</abbr>'); ?></a>
32 	<?php endif; ?>)</h3>

But the output i am getting is:
2 responses so far ↓ (Write yours or 31 Trackback 32 )

What the heck are those numbers 31 and 32, and why are they displaying there? if i take out trackback_url() they disappear.

Please help.

Thanks!
R