Warning dealing with Pluggable.php

I dont know how long this has been going on, i just noticed it today…I may have installed some plugins before this started happening, i dont really know…However, i went to ‘Manage’ and edit a post a saved awhile back…When i tried to filter my posts i would get the message below..

“Warning: Cannot modify header information – headers already sent by (output started at public_html/wp-admin/admin-header.php:16) in public_html/wp-includes/pluggable.php on line 390′”

Also…When writing a post i clicked on “4 more” to pull up some of my post drafts i have saved, and i would get the same message….can anybody tell me how to find this..