PHP error problem

I have a PHP code on a Linux server that is a PHP form, and when the form submits it returns with an error: Warning: Cannot modify header information - headers already sent by (output started at...) I realize that this is because there is something getting generated that is coming before the header but I haven't been able to track it down and don't want to take the time. In addition, I am looking for someone with experience that might be able to step in to work on occasional similar issues. Sorry if you read this previously and responded, I am new to Freelancer and posted it incorrectly! Please respond again.