Notepad++ is the answer to all your BOM pains

For some reason, with Dreamweaver (and maybe other editors), the BOM (Byte Order Mark) is introduced when you have not asked it to be... and only on some pages. It's a bug. Problem is, the bug makes your page invalid to W3C standards. The DW validation tool won't pick this up

Download and install the free Notepad++.
http://notepad-plus.sourceforge.net/uk/site.htm

Whenever the W3C validator throws up the BOM error, just open up the file in Notepad++, click on the 'Format' option, tick 'encode in UTF-8 without BOM' and then save your file. The BOM is taken out and your page is valid again.