Hopefully you're not in the subset of people where ANC causes headaches. Since they're designed to block out a lot of the lower frequencies in ambient sound, some people's brains perceive that as a change in air pressure. But since there's not the pain and discomfort usually associated with changes in air pressure, the brain actually CAUSES discomfort to encourage you to pop your ears. Obviously that doesn't get rid of the lack of low frequencies, so the sensation can get worse until you remove the earbuds. Some people can adjust to this and/or ignore it, others can't, and still others don't even have that problem at all.