It's all about visualizing myself being a swedish guy with a moustache
Naw. Well, what can I say? It's actually two techniques at the same time. In the lower growls I'm using false vocal cords to produce the "bra wl wl wl wl". There's also a bit of distortion all the time, but all the time when moving higher the distortion takes more and more of the sound and in the high screaches it's all about that.
The distortion is made somewhere in palate.
Vocal FOLDS? WTF. So are they "vocal chords", "vocal cords" or "vocal folds"! I'm shittin myself here! Now anyway, the distortion can be found with a "twanged" evil witch laugh. Overdoing that sound with loud volume, directing the sound from "out from your eyes" could make you find something. I can't test it though, I'm at work, te-hee.
The low sound is more difficult. Hmm... Well, try to imitate a purring cat first with your mouth closed. Then keep to sound going while opening your mouth. That's where it comes from, but in order to make it sound more death metal you need to put more volume and kind "muffle" the sound with your throat, and in addition use some distortion. The muffling feels pretty much like if there was a penis in your throat and you'd try to squeeze it. Most likely this will sound like shit no matter what. I know I do. The proximity effect of microphones is growler's best friend.
(The author of this message takes no responsibility of the possible exploding heads, terrible pains and forever lost singing voices.)