Shifter Vibration

My 93 si had an engine swap done on it and my shifter vibrates around 5,000rpms. The guy who swaped the engine has proved himself to be a moron so is there anyway that this is his fault as well as all the other stuff on my list that he is going to answer up to? It never vibrated and rattled before and its getting worse. The knock sensor code reading has came up from day one and that caused my catalytic-converter to go and for it to run rich. I hope one of you guys can give me some advise before i try to find the vibration. I would rather know where to start and what to be looking for....its always easier to take apart than it is to put back together.