Turned out the raspy, rattling sound was the alternator pulley. These are sophisticated "overrunning" pulleys with bearings etc. Replacing the pulley got rid of the loud noise.

Definitely sounds like the axle. I’ve had the problem multiple times on my s13.

Could it be the exhaust pipe bouncing against something?

any update on the problem?? mine is making similar noise

My s14 does the same noise, can it be the bearings? Cause it doesnt always make the noise only after so much vibration or driving for a while

He has aids. Looking for Delta 32 CCR5 bone marrow. it is the cure.

Hey Nolan, I sold the 240 before solving the mystery. My best guess after investigating is that one or more of the differential shaft bearings were bad, and allowing the output shafts (which connect to the axles) to vibrate and move.

Did you figure this out? my s13 makes the same noise...