When my parents decided to build a house, it was quite an ordeal.  According to my mother's apocrypha, my father decided to move because the floor in the kitchen squeaked.

It squeaked noisily. 

It prompted comments from guests. 

It shook dishes in cabinets. 

On occasion I noticed this squeak, but, to me, it was less than annoying. I suppose I’d call it part of the house's character. Attempts to fix the nefarious squeak were made but it persisted.

Dad couldn't live with the squeak, couldn't fix it, and moving became the only option.  Mom acquiesced.  The possibility of further squeaks remained, however.  Older homes, of course, contained immense squeak potential, and any home with a squeak-harboring appearance deserved elimination. Finally, after many realtors, I suggested building a house. A squeakless and squeak-resistant house.

Housing Contractor Mike Rigney (Documentary Photo #34dq1):

Houses squeak for a variety of reasons, but you'll never really know the exact cause until you rip up the flooring.