I would first look at the rad fan clutch.  They can make a noise like
that when failing.  If it is 'loose' when the engine is cold and off it
might be bad.  If you heat up the engine fully and watch while someone
shuts off the engine, it is supposed to stop almost instantly.  If it
keeps on spinning when hot, it is bad.

I would look at the heat shield on the Cat second.  It can have one of
it's anchor feet break loose which rattles.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
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