Approach to removing extra space at beginning of RSS file?
Someone left a space at the beginning of a module. 

[space]&lt;?php  


You can either try to find that bit of code with some tool or command OR put this in includes/bootstrap.inc at line 1112:

echo $filename;


The line number could change subject to updates to Drupal 7 so make sure it is inside the drupal_load function:

if ($filename) {
    echo $filename;  //this is your included line
    include_once DRUPAL_ROOT . '/' . $filename;
    $files[$type][$name] = TRUE;


The result will be a long list of the modules being loaded in source code of the page.  The space will be right after the module with the problem.