Menu error - line with these 3 characters 

in a production server choosing the pages from the menu I get this strange little error.
Between the menu and the loaded page, there is a line with these 3 characters 
Can anyone tell me what it could be?
Thank you

I don’t know why you have those three characters but they are the

Byte Order Mark EF BB BF

for UTF8 data, that is interpreted with the wrong charset (ex. ISO-8859-1)