What is the occasional crackling sound on an A330?
I have recently flown on a China Eastern A330-200 from Shanghai to Beijing and that noise was heard around 10.000 feet both on the way up and on the way down. It sounds awful! Everybody was rather worried, including myself who, despite being a frequent flyer, had never heard that noise. At first I thought it was some fatigue issue of the aircraft skin while "inflating" as internal pressure increased. 
But a few days later I flew on a Cathay Pacific A330-300 from Hong Kong to Jakarta, and after hearing that noise again, I asked a flight attendant who told me it was likely ice crystals in the air conditioning tubes that form when the outside air is very humid. She said she heard it many times and it's considered normal on A330's.