I am a frequent traveller 150K miles and up a year for 20 years and every airline has the same problem, the 3.5mm stereo/mono jacks! Problems from a plug has a broken jack in it, poor connections to high pitch squealing. It was really bad this past Christmas when my wife, our 2 kids age 5&7, went back to England to see our family and our audio was not working. We got vouchers totalling $100 USD for our next flight but the kids did not care and neither did the passengers around us when they started crying. Lucky I was prepared and gave them my iPad to watch Frozen and play games.
Surely I can not be alone here, who else has had broken to poor in-seat audio problems and what are the airlines doing to solve this problem?