I had an E&E outflow valve stick open the day I was operating on one air conditioning pack because of a write up and got the intermittent horn, same as take off warning horn, once in a B737. It took a few seconds to realize that the warning was also for cabin altitude above 10,000 ft which it was at idle thrust descending. Adding a little power and putting on the second pack fixed it. I remember a couple of years ago the crew talking to their maintenance people about the beeping but seems they would have figured it out as we did. I don't believe they would have continued climbing to high altitude with pressurization inop. Also why call maintenance unless you just thought it was an inop takeoff warning horn?