I have an AO Smith Aqua-air V100 that has started to make a humming noise that seems to be running very often but not all the time, does this mean that the unit is starting to wear out??

Let me explain the function of a bladder tank. Pressure and bladder tanks provide a air cushion that produces water pressure in your system so your pump doesn't kick on every time you draw a glass of water. A bladder tank has a neoprene membrane in the center. As the pump puts water into the bottom half of the bladder tank the membrane compresses the air in the top half. When the pressure reaches the cut off point in the control box the pump shuts down. However you still have between 40 to 50 pounds of pressure pushing the water out to your system. As the pressure drops in the tank when you make a draw the pump kicks on and everything starts over again.
To check, take something metal and start rapping at the bottom of the tank and work upwards. You will hear a "clunk" in the bottom half full of water. On the upper half you should hear a "clink" because the upper half should have nothing but air in it. IF the sound doesn't change or changes close to to tank top then the bladder tank must be replaced. Your air setting on the tank should be 2 pounds UNDER the cut in point in the pressure control box. If your pressure control has a 20 PSI cut in and 40 PSI cut out the tank pressure should read 18 PSI. The bladder tank setting MUST be made with the pump off and the system bled down by opening a cold water faucet after you shut the system down at the breaker box. I want you to check for a ruptured bladder and check the pressure in the tank after the power's been turned off and the system bled down. Let me know what you find. Hope this helps and thank you for rating my reply. Tom

SB is on the right track. The V100 is a pressure tank. What you mean to say, I think, is that the pump is running most of the time. If that is the case, does the pump tend to run even when no water is being used?