I wouldn't worry about it provided that the sound is consistent.
High pressure liquid refrigerant flows to the evaporator and boils off; some systems make more noise than others.
An intermittent sound would be a cause for concern though.
General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"