Yesterday I drove back to school which is about 330 miles. When I got back I heard my car making a rattling noise. Today I checked it out and it almost sounded like the engine was knocking but I changed the oil only 2k miles, but it was raining on my ride back and thought water could have possibly come up the intake into the engine so I decided to change the oil anyway. I let the engine idle for awhile and then put it in neutral to let the car roll of the curb I had it raised on. When I went to put it in gear it wouldn't go (its an auto). Finally around 2500 rpm it would move slightly and I could feel the hesitation and it catching slightly at times. I then just put it in neutral and rolled into a parking spot. I tried to put it in drive again and it went nowhere. Any ideas whats wrong? My tranny just done or possibly rear end or u joint?

 

Check fluids, oil, ATF per FSM. Report CEL codes.