I listned to this headphone in a store the other day and heard some insane ringing at higher frequency that I'd never heard before. It ruined a few of my favorite songs with a piano. Was it the amplifier I was listenign to or do you notice something like this as well?

I can't say I heard ringing myself although do hear a bit overly metallic sounding drums, electric guitars and vocals. 

Good review. I also enjoyed your youtube video. Would you say the LCD-2 also win out over the NH?

Just curious, how many burn in hours you have on these?  Different drivers, but with EL-8C I had this "metallic sheen" for the first 50-60 hours until it got smoother after 100hrs.  At 200hrs they were perfect!  Again, I'm talking about planar magnetic drivers, but nevertheless, extra burn in might do it a better justice...

@twister6 That's a good point. I did burn them in although probably not quite up to 100 hours. I also listened to them and thought they were getting a bit smoother. But then I switched to the Audeze LCD-3 and then back to the Nighthawks to compare. I think what happened is my ears were getting used to the Nighthawks instead of them actually changing much. 

You twice mention that the Nighthawk's are made in China, and state that this is a con. Your "very capable" Oppo HA 1 headphone amp is also made in China. So are products from Sonus Faber, Monitor Audio, B&W, KEF, etc. 
 
I am not sure what Audioquest's HDMI or Ethernet cables have to do with the Nighthawk. And you would not be the first person with an "engineering background" to say cables don't matter and expensive cables are not worth it. Furthermore, Audioquest has quality digital cables starting at around 30$. No one is forcing anyone to buy the top of the line cables.

I wanted to comment on the "made in China" observation. Remember when made in Japan automatically meant junk. That sure changed. We in the audio hobby arena need to accept that many of our future products will come from China. That does not automatically make them bad. I am aware that Chins is struggling through some of the same quality control issues that Japan did as they rampted up their electronics industry. The key will be to read reviews to tryh to sort out with some consistency which companies/products are doing well and which ones are falling behind. My guess is that with emphasis Audioquest puts on quality, the Night Hawks should be just fine in the manufacturing area.

Good review. Although, you literally listed "Made in China" under con.