PHP Includes Causing Margins

Good evening, everyone! I am in desperate need of help, here, as Google has failed me — I’m starting to feel like the only one with this problem!

This is a brand new issue for me, none of my other previous themes had this problem: in short, php includes appear to be inserting a random gap/margin at the top of the page, the bottom of the page, and in between divs that are part of includes.

Simple as that! Every time I have an include, it adds a strange margin, ehwther it’s standard PHP include or WordPress’ include function. (Bear with me, I’m brand new to PHP!)

What’s even weirder is that sometimes I can make the margin vanish by leaving the wrapping div out of the include — but it doesn’t work all the time.

Note: There is no CSS affecting margins on these divs except for margin: 0 auto;.

Ex:
<?php get_header(); ?>

wherein the header has:

<div id="branding">
     <h2>Header Info</h2>
</div>

will cause a margin gap at the top of the page, but:

<div id="branding">
     <?php get_header(); ?>
</div>

wherein the div remains outside of the header does not.

That said, my footer retains a gap at the bottom of the page regardless of what is going where.

Even more strange, Firefox displays this issue (as I imagine it’s displaying it exactly as it’s reading it), but IE7 does not. IE6 is not being supported, so no clue there.

Help? Is this a PHP 5 thing? That is the only thing that’s changed for me between my previous themes — Bluehost is deprecating support for PHP4 so I upgraded to PHP5.

Thanks in advance! I apologize for the length of the post.

All the best,
– Whim