97 Blazer-mo' transmission fun

Ok..couple of you have answered my tranny questions before-need more ideas...

When the truck is sitting still & I put it in reverse, there is a noise from the underside that kind of sounds like someone tapping on metal. I can shift into other gears & the sound doesn't go away but does decrease a lot.

I can't see anything rattling around, but I'm hesitant to goof around under there with the thing in gear too...

Ok guys....any ideas before I go to the shop & grab my ankles?

-Mike

try turning you driveshaft by hand back and forth and see if you hear the sound it may just be u-joints