help my sidekick

Question...when im driving around w/my sidekick, in 2nd gear it will start making a rumbling sound and it shakes the damn car! its pissing me off and i really don't know what could be causing it. yes im a newb and i havent really looked in the forums. help me out if u have any ideas. thanx

its a 97 4x4 1.8L

nevermind....i found out theres a missfire in one of my cylinders.