Ductwork pinging or popping. Should you listen to a pinging or popping sound coming from metallic ductwork, this may be due to thermal expansion or by air blowing earlier a free flap of metallic. More probably is the possibility that the tube or maybe the pump is clogged with algae. http://marcofigie.getblogs.net/25521342/the-basic-principles-of-ac-installation-contractor