Recently as the weather has gotten colder I noticed when the Geo-thermal heating system turns off it makes a loud bang sound in the basement. Upon investigating it, I see that the pipe that takes the water from my open loop system to the outside shakes alot when the system shuts off. I tried to add additional strapping to minimize this, but it still happens and it seems to be getting worse. Does anyone know why this is happening? Is there something I can do to stop or reduce this from happening? My father-in-law also has a Geothermal system and he says his bangs too sometimes when it shuts off.