If you're talking about the plastic container that holds steering fluid, then that should always be at proper level. A lack of proper level can result in a humming sound when using the power steering.
If you're talking about the box at the end of your steering column, that's the steering box. A clicking or ticking sound from that apparatus means that something is definitely amiss. Either inside the box or the box itself is loose. Either way, it must be checked by a good mechanic. Steering box problems if unchecked, will only get worse and is very dangerous.
ps. If the fluid is low, it means that you're losing fluid. This usually occurs in the power steering hose. A slight pin hole in the line and it will spit out fluid every time you touch the power steering.