clicking sound in reverse

I get this clicking sound in reverse - any ideas what this is (other than the CV boots)?

the only thing i can think of is possibly a bad spur gear. because the reverse gear is totaly differant in honda manual trans. all the gears except revers are helical cut. they are all curvy and such this allows for a smoot tranny that is quiet. and they are alot stronger. the reverse gear is just a gear that is straight cut and is very noisey. that little whur type noise you get when backing up is the gear. but it may cause a click i need more info though.

Could be one of your motor mounts, my car did that shit when I bought it, costed like 300 to fix.