Originally Posted by erienbooker
After flushing the toilet, there is a ticking in the wall? What is causing it?
In mechanical engineering, one of the things you learn is that static friction tends to be higher than dynamic friction. That is, if you put a steel block on a board, and then elevate one end of the board, the friction holding the block in place will be greater than the friction between the steel and the wood once the block starts to move. (Friction is one thing that every scientist will tell you that we simply don't understand well, or at all, really.)
One result that arises when static friction is greater than dynamic friction is "earthquake" type motion. That is, static friction will hold the pipe in place against the wood studs until the tension builds up sufficiently that it overcomes the static friction and the pipe moves. Since dynamic friction is less than static friction, the pipe moves until tension in the pipe is lowered and dynamic friction brings it to a stop (when static friction pins the pipe in place again). Then, tension builds up again, and it happens all over again. And, your cold water pipe does that dance with the wood studs in the wall every time you flush the toilet and it gets filled with cold water, causing it to shrink slightly.
It's this repeated "rubbing" contact between the cold water supply piping and the studs in the wall that you hear as a "tick" pause "tick" pause "tick" noise. The filling of the cold water pipe causes it to shrink slightly, and the rubbing against the wood as it contracts cause the noise. The very same thing happens in houses with hot water heating systems with the heating pipes rubbing against wood.