Hello!
Still getting used to our XC so please bear with -- last night while turning right the car made one, single, horrible, "thwunk" sound. Nothing else was affected in any major way that I could tell. My brain went into overdrive and I felt that the steering was a bit tight for a few moments.
Anything to fear? Should I have a shop look at something? What would that something be?
The best way I can describe the sound is like when a 4x4 gets the wheels turned too much and you try to accelerate through it. It was a definate metal binding type of sound.
Any thoughts/help would be highly appreciated.

I've experienced a similar sound, coming from the rear of my XC with 155K. It's best described as a hard thunk or series of thunks. It occurs more readily after a long highway drive. A Volvo Master Tech spent some time with me and he felt it as well. Have currently ruled out the bevel gear and the rear differential. The rear viscous coupling is currently suspect number one. There is a freewheel/locking mechanism inside that he suspects is sticking. The visous coupling is only available as one complete part and is fairly expensive. We're trying to confirm the problem before proceeding. Other than a driveshaft repair under warranty, my XC has had few problems since new and been a great car.

Wow on this car with your mileage it could be a bunch of stuff. start with swaybar links...to check them drive car straight then move wheel back and forth if you hear a clunk every time you move the wheel they are bad,second most common is ball joints check them on a hoist, look also for the retaining nut on the bottom of the ball joint backing off, unfortunately if this happens you still have to replace them. now the big one ... have dealer check the angle gear at the trans.,most of us call it a transfer case, as they are known to be a weak link in the Awd system. as far as the cv joints I can't honestly say I have ever seen one of them go bad on this car, although I am sure it is possible. hope this information helps.......good luck!!!!

try it and see if it does it again! If its a series of thunks then it could be the CV joint. How many miles are on this bad boy???

Hmmm? I thought CV joints made clicks not Thwunks.
The car has 104K miles.

I saw from an earlier post your car has 103k miles.....so your in that famous "danger zone" or "dollar zone" as some people call it here!