Have you tried another headphone set? I have one (admittedly cheap) set that works perfectly with my NC, but not with the iPad.
Getting poor audio quality when listening through headphones. After unplugging and replugging the headphones numerous times (have tried 3 different sets), I am able to get better quality, but it's trial and error. I also hear nasty popping between songs in the music player, like the audio is shutting off and on between songs. Any others having similiar issues?
If you've tried different headphones and you know they work well with other devices, then it could be a bad jack-it happens sometimes, so you might want to see about getting it exchanged. Just first make sure that none of these headphones are ones you bought that only work well with an iPhone, because it may be the wrong kind of headphone.
Another thought here is that the jack may be a bad jack on the unit itself. I too am experiencing popping and have problems with the headphones connecting. Am going to try another set just in case, but the ones I have now work fine with my NC. Might have to return.
Edt: I did find that you have to make sure and push the plug in all the way, further than you think you should since there's a lot of resistance to it. Once seated this way, I get a little bit of static when audio starts and stops, but no popping or loud crackling. And audio throughout playback is fine. Really loud when you turn it up.