Hello - 92, 4.0, 4" lift, aw4, np231

I have a really odd grinding/metallic vibration when I "blip" the gas peddle and let off abruptly. It doesn't matter whether in driving or sitting in Park. It is definitely coming from the front of the XJ for about 1 second anytime the accelerator is let off abruptly. I'm usually pretty good at diagnosing the XJ nowadays, but I can't sort this one out.

Motor mounts are good, flywheel was recently checked. It really sounds like a bearing noise.