We have a very large home with Zoned heating. Our furnace is a new installation but the piping in the walls and registers are original equipment. We have developed a noise in the system that sounds like the half moan/half whistle noise that wind makes when rushing through a cave. The sound is not coming from the furnace itself but the noise starts when the furnace kicks in. The system is newer, the pumps are oiled, and the system is bled dry of air. The tank was water logged but that was corrected too. What is making this noise? Does anyone have any idea?