Hey guys, ever since I remember getting my car I have this weird problem that sometimes, I say 1 out of 15 times that I shift into reverse, it doesn't really "click" and when I release the clutch I hear a slight grinding of the gears and no movement of the car. I proceed to clutch back to neutral and back to reverse and then it clicks and feels sturdy, and then the car moves normally.

What is this problem? Why does it happen? I actually did get it checked once and the mechanic couldn't figure it out. It just didn't happen when he tried it, and it's mostly not an issue (except maybe if I'm parked on a slope) so I'm just curious if this happens to someone else.