Exomious

Called a mechanic for a professional opinion. He thinks the most likely thing to cause this is the driveshaft or a diff.

I've got a 91 subaru Liberty LX, it has 290,000 km on it (about 180k miles) and hasn't missed a beat since I got it about 6 years ago at 220,000km. Until this past weekend of course... I was reversing out of our driveway, and just as I was about to go out onto the road, I head a clunk and it stopped moving, the engine was still running. I heard a quiet tapping sound for a few minutes before it went away. Now it idles fine like it did before with no strange sounds, but when I put it into gear, nothing happens. doesn't matter if it's 1st, 2nd, 3rd, 4th, 5th or reverse. It won't move, it doesn't make any noises shift still feel great, clutch feels fine. What makes me the most nervous is that I can shift into gear while the engine is on without the clutch so I don't think the engine is spinning the gearbox. But if the driveshaft is broken, wouldn't it make noise? I've checked the CV joints in case one broke and that's why it won't go but they are solid. I have picked up a 1990 Nissan Pulsar so I can take my time getting the subaru back on the road and do everything right. Any help is greatly appreciated.