Reverse anchor?

I have a 98 b series truck and one day when i tried to reverse it made a real loud clunk noise and then the reverse wouldn't work. when it is in reverse it has a little hum as if there are parts in side the tranny just spinnin....is this the reverse anchor or what? any help would be appreciated

Sounds like the shifter foot on the end of the rod connected to the shifter slid out of the detents. Most likely you would have to remove the tranny take off the tail housing put the shifter mechanism back together if nothing is broke and put the tranny back in.