Main causes for inflight cabin pressure changes...
Well, for me the ONLY reason is easy: Flying on a Tu-134
Twenty years ago during one of the many strikes at SAS I was on an Interflug (East German) Tu-134. It seemed to me that the plane was going steady and level at 27,000 ft (so the captain said - "siebenundtwanzig tausend Füsse"), but the cabin pressure was fluctuating up and down so I had pain in my ears for the next three weeks.
I have only had three flights on Tu-134, my first, last and only flight. Ten wild horses will not be able to pull me on board a 134 again.
Going home I changed my ticket to a Yugoslavian DC-9. Before that flight I noticed that the captain emptied a pint of beer in the transit hall bar and walked directly on the plane. And he didn't walk too steady. But man what a pleasant flight compared to Interflug. I guess that the captain took a nap in his seat and put the co-pilot to work. Isn't that what we have co-pilots for?
Yeah, that's how it was. Fortunately the good, old days have changed to the better.
Best regards, Preben Norholm