I noticed the same thing and just returned my HE400's, I listen primarily to rock and noticed during several songs that the vocals in the track seemed to be recessed while the high hat was overpowering. I think turning them up to hear the vocals caused the highs to give me tinnitus which I now have and won't go away. I've never had tinnitus from a hp before and don't listen at excessive volumes. I would love to see a real frequency graph to get a visual on what I am hearing to confirm it. I bought some HD600's based on a recommendation and to my ears they have better balance across the frequency spectrum. Interestingly I play bass guitar and I feel that the HD600 more accurately portrays what I hear coming out of my bass amp than the HE400 but then again I'm not a dubstep or hip hop guy and am not fond of synth bass. I had rev. 2's btw.
I got the one with white plastic rig, don't know which revision it is. I suppose they only send rev.2's now?
I listen mainly to rock (and its derivatives) as well. The Wall is in my burn-in playlist so I could listen briefly to few tracks of the album and this is clearly apparent. I think "muffled" is the best adjective to describe the vocals I hear... That's a shame, this album is pure wonder with the HE-500 :'(
I didn't recall the HE-4 to sound in a such way on rock... The mids were recessed too, but they were not so "muffled". That's too bad, the 400s are clearly the better headphones in a technical standpoint but I'm not sure I can get used to its tonal balance :/
I sent the 4s for repair (one earcup literally detatched itself from the head-band...) but when the replacement pair comme back I might do a quick round-up review between the 3, with the new velour pads, of course (I have 5 pairs).