Originally Posted by woodchuck
It happens more being on a well. Air in the water will collect in pockets in the pipes and in the top of the water heater. When the air comes out the sudden burst of air causes the pipes to shake hitting the places where it's a little loose.
Can't believe I have never had this problem (new one on me). Been on well system for 65 of my 66 years, now water logged tanks from before we had bladder tanks, yepp.
I would say it is just the pipes streching from the temp. change, I have that problem with the PVC stack on my furnace.