header - Problem with PHP readfile() dumping binary data to the browser

I trying to force a download by the browser here is my code:

header("Content-Type: application/force-download"); 
header('Content-type: audio/mp3');
header('Content-Description: File Download');
header('Content-Disposition: attachment; filename=' . $file_name);
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
header('Content-length: ' . filesize($file_path);
ob_clean();
flush();
readfile($file_path);
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This works perfectly on my local machine, but when I upload it to my live server, the binary file is dumped to the browser and those gibberish characters fill up the browser window. What could be the problem? I am on a shared server so I don't know if my apache configuration needs to be changed or something.

I took @sanmi advice and used Firebug to see the response header and here is what I got:

Here is what I got sanmai: 
Server  nginx/0.7.67
Date    Tue, 06 Sep 2011 15:02:03 GMT
Content-Type    text/html; charset=UTF-8
Transfer-Encoding   chunked
Connection  keep-alive
Expires Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control   no-store, no-cache, must-revalidate, post-check=0, pre-check=0   
Pragma  no-cache
Vary    Accept-Encoding,User-Agent
Content-Encoding    gzip
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I can see that the content-type entry has changed to text/html, and that the server is actually a nginx one. So is this a nginx issue or are my header entries wrong?

Thanks, Tsega