I have two Hot Water Storage Tanks heated by Indirect Fire Method. Lately Cold water pipe going into Storage Tanks (Shown in Picture link) is banging very hard that i can hear that noise from two floor above 300 feet away. I have also attached MP3 file link on recording of actual noise. It appears that when cold water being filled to Storage Tank this pipe are banging because water seems to back flow heavily due to high pressure. My main cold water pipe pressure is 50 psi. Not sure what exact pressure at water tank level. When pipe hammers, if I open any of the hot water valve open at anywhere in house, it immediately stops hammering but it again starts after 5-10 minutes. It is doing more on late night when we are sleeping than during day time. May be because we use water which releases the pressure.
Can someone please help me understand what could be causing this issue and what can I do to fix it permanently ?
1) Picture of Indirect fired Hot Water Heater Storage Tank: https://app.box.com/s/2yixrskgxcvltlozkh9j
2) MP3 Sound File Noise coming from Cold Water Pipe Shown in picture: https://app.box.com/s/2htd4crc8z4mlr23igz6