Using Eloy's grep trick on the lang files revealed a lot of BOM markers. I assume they don't cause any problems in html files, but I think that the php files can be a problem.

For absolute vi dummies like me, the solution looks like
grep -rl $'\xEF\xBB\xBF' * //Search folder and subfolders for BOM markers
vim filename //opens file in vim
:set nobomb //removes the BOM
:w //saves the file with the same name
:q //quit vim

(credits to Eloy and http://www.tuxfiles.org/linuxhelp/vimcheat.html)

to perform on a *nix or a mac.