It just started happening a week or two ago. When any of the fixtures are being run more than say halfway open (hot or cold) there is a groaning noise in the pipes. It almost sounds like a gas powered line trimmer idling in the wall. I've narrowed it down to a corner of the house, but I think it might be in the wall.
After looking online some, it's my understanding that this could be a loose fixture or washer and when you run water somewhere it reduces overall system pressure on that point which lets the thing vibrate a little. Or...something like that.
Is there any trick to finding the culprit?