I was under the impression that the ringing on the Vali is never eliminated completely.
I am using HD800's. When I plug in the headphones, I hear fairly low level ringing that goes away after about 15 seconds. To get louder ringing, I have to tap on the case pretty hard with my fingernails. If I tap with just my finger, I don't get any ringing.
I am totally OK with this amount of ringing. It's generally so low level that even when there is ringing and you have music playing, you can't even hear it. My previous unit would ring so loud when I touched the volume knob that you could hear the ringing loud when the HD800's were sitting on the headphone stand.