FileETag None
<IfModule mod_headers.c>
Header unset ETag
</IfModule>esta es la manera de excluir el campo fileetag de la respuesta del servidor:
By default, both Apache and IIS embed data in the ETag that dramatically reduces the odds of the validity test succeeding on web sites with multiple servers.
«Configure Etags» de Best Practices for Speeding Up Your Web Site.