motor mount? check those. with the car running (congrats on fixing it btw!!!!) have your right foot on the brake and your left on the clutch. slowly let out the clutch but not enough to let the car die but as to just engage it. if motor mount is bad the engine should "rock". i would say balancing of tires but you mention that you can hear and feel it under the car.....what exactly can you hear....and feel....what speeds.....accelerating ...braking?