2002 Cadillac DTS the vehicle shakes when on and parked.

hi, ima little concerned about my caddy. the car does not have any warning signs on the dashboard drives great and does not stall at all however when im at a light or parked, my car shakes slightly. in addition to that, when changing from park to drive, neutral and reverse my car jerks slightly. im pretty sure this isnt normal as ive driven other cars that don't jerk at all. what could cause this, are these symptoms to a bigger problem? thanks.