I have a Nikon AF-S Nikkor 70-300mm 1:4.5-5.6 G ED Lens that I purchased in Feb of 2013. I have been using this lens with my Nikon D3200. Up until this point my lens and camera have been completely fine. However, my autofocus suddenly stopped working. I know it is not my camera as my autofocus works with every other lens I own. I keep my lens all very clean, I tried resetting all my options to factory resets, the lens has never taken a hard fall, and yes it is set on M/A. When I try to autofocus I can hear my camera trying to focus, but nothing happens. What is the problem and how can I fix this? I really need this lens!
You should not be able to hear your camera focus because your camera doesn't have a built-in focus motor. Therefore, you are hearing the lens focus (or at least the motor inside).
So, you can hear the motor in the lens but the lens elements don't move so you get focus. I would from this assume that there is a mechanical defect in the lens.
The above only holds, if you are actually hearing noises caused by focusing. Other reasons I could think of are that the M/A switch is in the right position but not working. Try toggling it a few times.
What you also could be hearing is image stabilisation (IS)! On my copy of that lens, this is much louder than focusing.
If it is indeed IS that you are hearing, then all options for what is wrong are on the table, again.