What noises are considered worrying on a passenger flight? As a typical 'nervous flyer', I often find myself asking crew about a noise that they say is completely normal during flights. The thing is, I've flown a lot and still hear new sounds sometimes!

For example on a recent Easyjet Airbus flight, when the aircraft went into full throttle to take off, a loud whirring/buzzing sound started and lasted the whole flight (I was sat on the wing)... still no idea what that was.

So what is a general list of sounds that are to be expected vs a list that tells you that you are all but doomed :/

Let's keep this to an Airbus Easyjet might use to keep it a short(er) list.
The only noise (other than a clear and obvious explosion) that gets my complete and immediate attention is "This is the captain..."