I have a 06 and after I changed the fluid to the Fuchs brand synth it almost stopped the RSN completely. It doesn't even happen if I try to make the noise- ie very low rpms. the difference is night and day 247k on the tranny
DARF involves drilling a small hole in one of the transmission plates. When I got my 2004 serviced, Amsoil transmission fluid was used and the rumble is much, much worse when the transmission is cold; but I can't afford to have the DARF done.