Vauxhall Corsa loud noise when starting car or turning off ignition

Every time I start my car, there is a really loud noise (sounds like a childs toy gun being fired) and it lasts about 30 seconds. It also happens when I turn my engine off. The car seems to be running OK and it doesn't continue when I drive. Not sure if its connected but when the passenger door was open and the interior light came on, when I pressed the button to open the window, the light started flickering. Is my car safe to drive, any ideas what the problem could be and how to fix it.