1986 Ford Mustang Clutch or Transmission

I hear a grinding noise in my clutch or transmission. It sounds like something is loose. While idling with the clutch out, it grinds. I have a 5 speed. It grinds in first, second, less in fourth, and less in fifth. The grinding noise has gotten worse in the past two weeks. Please let me know what you think the problem is? I don't know whether I should drive it or not because it sound like something will fall out. My 1986 Ford Mustang LX , 5 speed, with a 302 engine. Please help!