The noise is coming from the transmission or lower engine area. its a strange rattling noise that increases as the motors revs up but will then stop after about 4 to 5000 rpm. No occurrence during high speed mainly at take off and lower speeds and gears. Its kind of loud though. Thought maybe a spun bearing or something. no problems shifting, grinding, stiffness, nothing like that? I dont know if its in the motor a clutch or transmission problem any help?

Do you have enough motor oil in the motor if you do you may have a bad oil pump , but before you change the oil pump check the oil pump strainer in the base pan I hope this information helps you

if this is under the hood (front of car), it could be an exhaust heat shield that is either corroded loose or a fastener has come loose. Does it happen when you rev the engine in park? if so, either have someone rev while you watch for whatever is rattling or have them watch while you rev.

Could be a long list of things.
A mechanic would take a test drive and listen under different conditions.
Causes could include transaxle problems, exhaust rattles, worn motor mounts, even valves in the engine.
The difference in idle and moving is a load on the engine and transaxle and the engine shifting position.

it could be a wrist pin, and im not sure if those amc's had hydraulic lifters but sometimes with old lifters when the oil pressure is lower at an idle the lifters arnt filling up all the way so they develope a little valve lash, and when the rpms are raised the oil pressure raises and fills the lifters. you could try chasing the noise down with an automotive stethoscope.

Just a couple ideas...
Your engine and transmission will shift slightly when in drive, and maybe that movement is allowing it to rub on something. Another issue may be that the noise is actually from the transmission.
Torn motor mounts will allow the drive train to shift or move farther than normal.

Inspect the motor mounts for cracks or breaks in the mount. Ask a friend to stand at the right front fender with the hood open while you start the car. Make sure the emergency brake is on and you block one of the rear tires in front of it and in back of it with a brick or similar solid material. Put the car in drive (1st gear for manual transmission) and with your foot on the brake pedal rev the motor for a few seconds at about 1500-1800 rpm as your friend watches for excessive left and right movement from the engine. Then do the same in reverse and have him stand on the left side and do the same. If one mount is bad it is recommended that all the engine mounts be replaced. There are usually 2 or 3 for the engine and one for the transmission.

check the exhaust pipe at the front of the engine there is a heat shield sometimes rusts at the spot weld and the shield rattles on the pipe
easy repair use a hose clamp open the hose clamp up put the clamp around the pipe reconnect the hose clamp slide it over the heat shield and tighten the clamp up

sounds silly but have you looked for a stone/nail in the tyre tread.strange noises are a bt s t rd to diagnose.......

When catalytic converters go bad, the porcelain matrix inside comes loose and is noisy.
But you can just unbolt it, break up the loose chunks, pour out the pieces, and it will run better than ever.
If you don't pass the next emissions test, then replace it.

But it could just be the heat shield rattling instead.
Take the shield off first, to see if it goes away.

Have the catalytic converter heat shield checked. Sometimes they vibrate loose and caus strange rattles or buzzing noises.