escort with rocks in clutch?

i have a 94 escort wagon which has been running great since i got it last year. today was no exception, and i made it to work without any incident, but as i was parallel parking,my car jolted just a little and the idle altered. i didn't think too much of it as i was late. however, as i was leaving work to go home for lunch, a strange noise that sounded somewhat like rocks bouncing around in my engine started accompanied my start and then consistently happened whenever i shifted in any of the lower three gears. the car feels even worse in reverse, and the noise becomes more intense and accompanied by shaking. all fluids look fine and although my gas was a pretty much on empty, i dont think that would affect my car in this way. any guesses?