My 2004 Saturn Ion 3 rumbles or shakes when I turn it off. What could it be?

What is your question?

I have had several things done since last August, when the check engine light came on but the last couple of things where the ignition coil pack and module, the cat. converter. The car does have 225,000 miles on it, not sure when the transmission or engine has or ever been changed could it be any one of those?