Weird Grinding noise under load

I don't get to drive my XJ as often as I would like any more. But every chance I get I take it. Yesterday I needed to move some stuff around between my house and my parents house. I used my trailer which is a 2 place ATV trailer. I didn't have to move anything heavy, just a little bit of wood and a table saw. Nothing too tough. Nothing the old XJ can't handle. Well, after a long day of back and forth in 95 degree heat I started to get this grinding noise while I was accelerating. But it would only make the noise if I gave it more than half throttle. It sounded like it was coming from the rear of the transmission or the transfer case area. I don't have any carpet anymore and the noise was pretty loud. Anything less and everything was normal. When it started making the noise I was pulling my trailer empty. I got home, unhooked the trailer and drove around some more. Still did the same thing. I found a dirt road, it made the same noise in 2wd, 4hi, and 4lo going forward. But it wont make the noise going backwards at all. No matter how much I get after the gas. It doesn't seem to be a noise coming from the engine as it doesn't make the noise if you rev it up in neutral. I am guessing something from the transmission or Transfer case. If I had to make a guess, I would say that it is the chain in the transfer case banging around. But it doesn't seem to slip and 4wd works great. And it make the noise in 2wd. I have done some searching on and I can't really seem to find anything that is just like my problem. Any advice would be great.
93 XJ 4.0 AW4 NP231 140,000 miles stock suspension

Update:
I got under the Jeep today to scope things out. There was nothing obviously wrong except one of the exhaust hangers wasn't hooked up correctly. So I thought that maybe the noise I was hearing was the exhaust rattling against the cross member that supports the transmission. I wired it up and took it for a drive. At first I thought that was the problem. But that was short lived because as soon as everything warmed up, the grinding noise came back. Here are some new observations. It grinds in more than just first gear. I have to be on the gas pretty good and the RPM's need to be up near 3000. The grinding seems to stay pretty constant and doesn't really seem speed related, but that just doesn't seem right. When I got home I blocked the wheels and put the transfer case in neutral and the transmission in drive. I got under the jeep and I could hear a noticeable chatter coming from the transfer case. I got a screwdriver out and used it like a stethascope to confirm it. It makes the noise in drive, but not in reverse. That is where I am at so far. I think that I am going to work on pulling the transfer case so that I can open it up and see what is going on. If anybody has any ideas or advise, I would appreciate them.

have somebody site in the back seat and drive a round have him or her try to pin point it out I have a noise like that and thought it was coming from the trany my budy was in the back and he said it was coming from the rearend

Just throwing an idea out there. I read of a bad pinion gear making a noise in forward direction, but not in reverse direction. Jack the rear up and disconnect the driveshaft and spin the wheels. See if it makes that noise.

Mine made a gawdawfull racket under load until I replaced the rear leaf springs. Are your springs flat? Do they have negative arch? First time I heard the noise I swore up and down the pinion was shot. After some time I noticed the shiny spot on the diff housing where the exhaust was hitting.

HTH

Here is an update, and boy do I feel stupid. After many attempts to figure out exactly what the noise was, my uncle and I were able to pinpoint the noise. About a year ago I replaced my exhaust manifold with an APN header. While in there I noticed that my motor mounts were shot. So, I made a quick trip to autozone and bought what they had. Turns out the rubber in them are so cheap they have melted and deformed. And when the under hood temps get hot enough the rubber goes so soft that under a load my engine was flexing and fan would start hitting the plastic shroud. So I guess some new motor mounts are on the list next. Does anybody have any ideas on who makes some good motor mounts?

Bought mine at NAPA. Nothing out of the ordinary but they did the job just fine.

ajporter03 said:

Here is an update, and boy do I feel stupid. After many attempts to figure out exactly what the noise was, my uncle and I were able to pinpoint the noise. About a year ago I replaced my exhaust manifold with an APN header. While in there I noticed that my motor mounts were shot. So, I made a quick trip to autozone and bought what they had. Turns out the rubber in them are so cheap they have melted and deformed. And when the under hood temps get hot enough the rubber goes so soft that under a load my engine was flexing and fan would start hitting the plastic shroud. So I guess some new motor mounts are on the list next. Does anybody have any ideas on who makes some good motor mounts?

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brown dog off road. half the price of M.O.R.E. and you can get them in rubber or polly. quality pieces, and you can buy just the bushings if they ever wear out again.