grinding noise in first and reverse

hey fellas i have a 2001 cherokee sport aw4 np231 with a grand cherokee fornt lp30 and a ford 8.8 in the rear.
i have a grinding noise that comes under hard accellerations in first or reverse. it only happens sometimes. im fairly certain that the unit bearings are fine although i did notice some black grease on the back sides of them when i did the gc30 swap recently. the xj only has 55,000 on it and the trany has been well maintained. also the sound seems to be rotational.

Just dont use those gears and you should be fine.

Seriously though, it could be a stretched transfer case chain. If it is and you let it go too long then you'll have a nice hole in your aluminum case.

Might not be it, but its a possibility.

Not likely the transfer case since there is no load on it in 2wd.Sounds like u-joints or possibly the slip yoke needs greased.

I could be very completely wrong, but doesnt the chain still turn in 2wd? Mine (with 230+k on the clock) was grinding if I would punch it a little bit in reverse.

I changed out the trans/TC combo later for a different reason and the problem was gone.

Like I said, I could be way off, but I think thats what mine was.....sounded like I was driving up tiny stairs really fast, and it was jerky.

Im interested to find out what makes a grindy noise, be sure to post results.

Could be getting some axle wrap and issues with the pinion angles with the hard acceleration.

mine was makin a funky grindy clunky noise takin off in first due to a completely dead trans mount

I had same thing. It was my t-case. Changed it out and noise was gone