I know what you mean.
I was debating between Sony m3 , Bose QC, and the new NC700.
After using all 3 I thought that was really annoying that I can hear these slight sounds. Yes even the new NC700
I don’t think there are any noise cancelling headphones that will block out sound 100%.
I thought I might as well use my Vmodas since they block out sound decently.
The result is Noise cancelling provided a better listening experience since I could listen at low volume with no distractions. I tested them at home since I have noisy neighbors and at the Gym since I do not like the music they play. I used to blast my Vmodas to drown out the sound. With my Sony M3s I can enjoy music at a low volume and it feels like I’m in an elevator, lobby, or library.
I realized that it’s because I focused on looking for sound. Once I focused on listening to a song and took off the headphones it was evident that a lot of noise was being blocked out.
My end result was I bought Sony M3s because I paid $220 vs NC700 being $400+.