Reverse sounds like a roller coaster... tranny going?

So I start backing up out of my driveway today and I notice a clack similar to that of a rollercoaster's chain drive (intermittent clacks ever second or two). It seems like it might not fully be going into the reverse gear (Its a 5spd manual tranny).

Anyone had a similar problem/or know how to fix it?

Well, I had an issue like this on a old VW GTI, it was a chipped toth on the reverse gear, but I have never heard this before with a Jeep trans. The last time I heard a sound like this was my transfer case chain met its end.. Were you in 4wd at the time? The other time a leard a similar noice was when I was in 4wd, and my linkage was out of adjustment, and the 4wd was not fully engaged, and it made a sound similar to what you are saying...

Got it looked at by a mechanic, sure enough I broke off a tooth on my reverse because my tranny fluid was full of water..