I have a 2006 Yamaha rhino 660 that makes a clanking grinding noise coming out of the middle drive. The U joint is in good condition. It does it going down hill

You probably have a bad right side C V shaft. The shaft has a spline joint in the middle; over time water gets inside and rusts the splines causing it to slip(makes grinding noise), and it will not turn the wheel, causing the wheel speed sensor to cause the traction light to illuminate. Replace the C V shaft (reman ones are really cheap)

Could be bad u-joints, wheel bearings. Raise rear of vehicle and rotate wheel by hand, if noisy remove and replace. Hope that helps.

Accelleration noises of the magnitude you descibe makes me think the engines crank shaft bearings have gone. Has the oil pressure light come on recently and what's the oil level like.
Without being there to hear it, it's very difficult to diagnose. You should detect noises and rattle if you rev it when in neutral if it is the engine. If the engine is smooth in neutral and the oil is good you may have a bad diff or cv joint

GET IT TO A MECHANIC!! Something is loose or about to collapse! Remember that vibration and noise can travel away from the source so get the mechanic to start in that corner.
You need to get the following checked!
-Prop shaft mountings at transfer box.
-Prop shaft mountings at differential.
-Prop shaft bearings.
-Differential condition and oil level.
-Drive shafts at differential end.
-Drive shafts at the wheel end.
-All flexing joints in the system including UV joints and CV joints.

It can vary from u-joints to the ring & pinion. You will need to apply pressure to the DRIVESHAFT to inspect the u joints for looseness. Generally u can move the driveshaft by hand when the trans is set in nuetral to check the ring & pinion for noise
Turn it back & forth quickly to hear any noise

Get your differential fluid checked and make sure you get synthetic for the rear if indicated. The clanking on turns reduces the possibility of the U-joints being the culprit. The driveshaft would give you noise going from reverse to drive, but in turns it is likely the clutches in the rear axle.

A four wheel drive can cause noise in all directions if the front drive has bad joints.

No,it's not either. I wouldn't recommend driving the jeep in 4wd until
you get this resolved, unless you want to spend big money on a new
tranfer case? The transfer case gears are not lining up properly,due to
either the shifter linkage not properly adjusted, or the transfer case is
shot, gear wise.U joints and cv joints(constant velocity) don't make
crunching noises like your explaining when bad. U joints usually just
drop the drive shaft when bad and you will go nowhere. CV's make a
clanking,rapping, or grinbding sound when bad. Good luck. Get it
to someone who can diagnose the issue , before you wreck the transfer
case, immediately.Good Luck.

CV joint is going out

The sway bar linkage probably came undone on one of the sides. Wikipedia has a picture of what your sway bar linkage may look like:

http://en.wikipedia.org/wiki/Sway_bar

That is a picture of a Porsche sway bar, but the idea is the same. Make sure all bolts are tight and that one end is not missing the linkage that connects it to the spring/strut. The grinding of the brakes may be the sound of the linkage piece touching the rotor. Sway bar is a logical solution to both issues.

If that doesn't fix the issue, put the front end of the truck on blocks or jack stands and have somebody wiggle the tire up/down and side to side while you inspect the mechanical components underneath. Other things to check may be the ball joints, tie rod ends and suspension bits.