I have a 1979 Z-28 RS and I may be able to help you.For I have rebuilt my tilt column in the past..Is it a tilt column? Or a column shift ? pictures would be a help.

 

Sounds like the tilt rod/cable alright.

 

Actually I have determined what the rattle is. It is the neutral/park rod coming up the steering column into the key cylinder. I can feel it bouncing and vibrating inside the column. The gear shift would be difficult to get in to park and the key would not turn back all the way so I could not get the key out so I just turned the steering column by hand counter clock wise to release the key lock. I detached the shift link rod in the engine bay and took it for a drive and voila... no noise.. as soon as I connected it back and went for a ride the rod in the steering column rattled and vibrated. So I went under the car (sucking my gut and squeezing under it lol) and found the shift link rod was loose at right at the tranny shift lever. So I tightened it and the rattle went away only 50%. So I know what the problem is... I just can't figure out how to completely eliminate it.