After I drive for about and hour or so, I get this grinding/rubbing noise when I try to downshift. The transmission upshifts just fine with no grinding or anything. It's only after extended driving that I get the noise. Usually, it refuses to go into the lower gear for a few seconds, accompanied by the noise, then goes in. I have tried changing the fluid, but no luck.

This is not the same noise that the T-56 cars are famous for when starting out in first gear. From what I see, that noise is normal.