I went through like 15 pages after searching but couldn't find any that matched mine.
I have an 04 z. Problem started after I replaced the motor. I couldn't get it to start so I took it to the dealership. They said my flywheel was on backwards and I laughed and said bs. Anyway, they dropped the tranny, did what they had to and my car started and ran fine until about 10 minutes before I got it home. During normal shifting is grinds all gears up to 6th. The grinding happens when I try to put it gear. There is slight resistance and will grind for a couple secs ONLY if I try to go right into gear. If going to 2nd I have to wait a for the rpms to drop while clutch is disengaged to put it in.
Another thing. When reversing sometimes, it's like a "clunk" then all the sudden I lose all gears and my tranny will be constantly making a grinding noise and its loud. When it does this, I have no gears. When i push the clutch in and try to engage any gear it grinds even louder and wont let me engage any gears. The only thing i can do is turn the car off n on and it will be fine. It also does that if I'm "coming" to a stop in neutral. Tranny will just starting making a constant grinding noise and i have to turn the car off and on.
The car will grind in neutral when I rev when the said above happens.

 

Nobody has any ideas...?

 

sounds like drive shaft to me

 

I shouldn't get resistance going into gears from a driveshaft....

 

Almost sounds like the clutch pedal cable isn't calibrated correctly - if the clutch doesn't fully disengage you can get out of gear but putting it back into gear will be met with resistance. About the sound - the Z tranny is loud but I'm not sure what that deal is with turning the car off to get it in gear. Could be related to the clutch not disengaging and continuing to spin.