1994 xj. 183k miles. manual trans.
makes a rattling sound under the shifter/ slightly in front of it when in motion, progresses into kind of a grinding sound at higher mph. sounds almost exactly like an ice dispenser grinding up ice. i can feel it in the shifter and pedals. a little bit in the floor board.
sound is only affected by speed. doesnt change if its in gear or coasting in neutral.
could this be the transmission mount? a bearing somewhere?

 

Sounds like the throwout bearing is bad, have you ever put a clutch in it? May need to look into that

 

clutch got replaced 60k ago after (previous driver's story) the clutch fell out on the highway..

 

Could still be throw out bearing if its been in mud alot, or tcase chain I would Jack it up on stands and make sure it don't fall and stick it in gear and look for the noise

 

Does depressing the clutch change the noise? Is your transfer case properly filled?