Hi everyone, I'm hoping someone can help me out... This is my first post... Recently I have been hearing a random knocking noise coming from my basement.. It only knocks like two or three times, then it stops... and it'll do it again like maybe 5-6 hours later. By the time you realize it's doing it and you run down to see what it is, it's done. All I know is that it sounds like someone is banging on a pipe. Does anyone have any idea what this could be? We're not running water or flushing toilets or doing laundry or anything involving water when it does this.. I'm just at a loss.