Grinding when letting off gas

[murray_xj]

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.

[XJ Wheeler]

I would try to blip the throttle from the tb under the hood, and listen. That way you can diagnose it easier being able to tell a little better. Past that, a mechanics stethoscope (or long screwdriver to your ear) will really help.

Sent via messenger pigeon - i talk, he types.

[murray_xj]

Thanks for the suggestion. In quickly doing so, it seems to make the same noise only shorter on the acceleration side before letting off as well.

It's certainly not a component i.e. water pump, alternator. The sound is mid to rear of the engine. Probably not good lol. No ticking or knocking any other time, very low oil consumption.

[bruggz351]

No pretty bits in your oil??

We had a bloke over here had a skirt fall off one of his pistons....

[BlackYeti]

Have you tightened your torque converter bolts yet?
Does the noise change pitch if you feather the gas while you are coasting?