Think this is U-Joints?

I was cruisin pretty good down a back road yesterday, and all of a sudden I heard a small bang noise and my manual transmission fell out of gear. I slowed to a stop right away because there was a grinding noise coming from what I think to be behind the tranny.

I figured something like this was going to happen, because about a week ago my car started making a terrible driveshaft noise while taking off slowly in first gear. I don't think there is any way this can be a driveshaft problem though, because I installed my frpp aluminum ds only about 10,000km ago. And new u-joints came with the driveshaft as far as I can remember, but I guess it's possible the bearing could be worn by now?

I'm told my T-5 has the typical problems it should for its age and mileage, grinding the odd time into 3rd gear, and the odd time slipping out of 2nd gear on deceleration. But it just didn't seem to me like this was my tranny on it's final legs, and more of a drivetrain problem directly behind it.

So what do you guys think? U-Joints?

I thought the driveshaft did fall out at first, but once I checked then everything seemed to be fully bolted in. I guess the u-joints that came with my frpp aluminum weren't greasable? Does that sound right? Or will an imbalanced driveshaft also make noises like that when you slowly take off in 1st gear?