I have somethimes a strange plopping in my left jaw when I open my mouth and sometimes it's not plopping and then my jaw starts to hurt when I'm opening it at the same range. When it's plopping it reminds me about snakes because they can unlock their jaw from their mouth.

You need to see a Dentist - it could be anything.

It definitely sounds like a problem with your joint. You should definitely see a dentist to have him/her check it as it could lead or be arthritis.