What the title says. It sounds like I put a bunch of rocks in a blender and hit it on high.

But it only makes this noise when I depress the clutch in any gear even in neutral. However, the noise does go away after reaching speeds above 8mph.

Does anyone have a suggestion on what might this be?

 

do a search on "marbles in a blender"

so many threads on this

 

i don't think that's the marbles in a can thing. sounds like your transmission is fubard. sux.

 

Either a bad clutch release bearing (i.e. "throwout bearing") or a finger broke off of the pressure plate.
The pressure plate fingers seem to wear pretty badly. Mine had some pretty deep grooves by 50k.