Hello, this is a combination of the metal in the water heater expanding and contracting due to the heat being applied from the gas flame. The heating tube runs through the water and heats. As it heats it expands, thus causing noise. The water is also drawing heat from the tube and can cause it to cool and this also will cause the cracking noise that you hear. This is a normal sound and is nothing to be concerned about.
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Hello, this is a combination of the metal in the water heater expanding and contracting due to the heat being applied from the gas flame. The heating tube runs through the water and heats. As it heats it expands, thus causing noise. The water is also drawing heat from the tube and can cause it to cool and this also will cause the cracking noise that you hear. This is a normal sound and is nothing to be concerned about.