I recently turned on my macbook only to find a gray screen with a question mark on top of a folder icon and some ominous clicking sounds coming from under the keyboard. After a few tries however, the system booted normally and the clicks did not occur again. On the mac forums, I read about many similar cases with the crucial difference that those users were unable to start their computer at all and that they had for the most part lost all their data.

Since the gray screen incident, I haven't dared switching off my macbook for fear it might not make it at the next startup. Is my computer in actual danger? Should I back up my files immediately and/or bring my computer to an apple shop for repairs?