Took off my front driveshaft to confirm that it was the thing making a huge clattering racket underneath there. Nice and quiet now. I need to measure it for a replacement. I'm thinking about going with a kit from Carolina Driveline.
'99 WJ Limited 4x4, 4.0L, Patriot Blue Metallic, IRO 3" springs, track bar, and rear sway bar links, Doetsch Tech 8000 shocks, Tenneco steering stabilizer, Carolina Driveline double-cardan front drive shaft.