I would pull it out and take a look at it, if you feel comfortable doing it. If it looks like there is a bur or scratching on it, then it is hanging up on something. Not knowing your experience level, i would recommend taking it to a gunsmith to repair. Should be easy and inexpensive.
If you do not see any wear, then I would just click it on and off about 500 times while watching tv and see if it improves. Take this advice with a grain of salt, since I am in no wayu a gunsmith, but it is what I would do.