Henry's car radio thing is spot on. That's the exact feeling, just with a floor. You know if you pull up that one board, the whole house of cards comes down. Suddenly you're not fixing a dip, you're redoing the whole foundation. The radio trick would be blasting music so you don't hear the floorboards creak.
Ever have that with a car? Like you hear a weird noise but if you fix one thing you know you'll find three more. Makes you just want to turn the radio up.