I noticed on both of my CO flights yesterday (EWR-SEA on a 737-800 and SEA-ANC on a 757-300) that when I plugged my headphones into the seat jack there was a constant beeping kind of sound coming from the jack. If you turned up the volume loud enough it would drown it out, but since I had noise-cancelling earbuds I couldn't turn the volume up that high without it being painfully loud. I tried it with and without my airline adapter, and I didn't have anything like that happen when I used my headphones with my iPod or on my DL flight last week. Does anything know anything about this?