Why does my car keep locking up.

What is your question?

When I'm driving my car keeps locking up on me and actually stops for a quick second before going back to normal. It's almost as if I'm hitting the breaks suddenly, but I'm not. There's no pattern as to when it happens. I've gone a week or two when it doesn't happen or days when it'll happen at least twice. It's at the most random times. It's happened to me when I'm on highways and even stop signs. I don't think it's triggered by the break because it's happened when my foots is or isn't on it, same for the gas petal. Each time it does it there a very loud sound, almost like gears.

How long has your 2006 Pontiac G6 had this problem?

Since I purchased the vehicle used.