Why do mattress innersprings go "pyoing" without provocation?

Question

I only notice it a few times a year, but just occasionally I hear a "pyoing" sound (like a spring being plucked) emitted from inside my mattress, even though there didn't seem to be any sudden movement that could have caused it. Why does that happen?

Answer 1

Favourite answer

One of the coils was squinched down the last time you slept or sat on the bed; it finally popped back up.