My 98 volvo XC is currently in the shop to replace the bevel gear and drive shaft = $3000
I bought the car 9 months ago with 95k miles. Shortly thereafter, it started making odd clicking noise/bouncing movement when turning. Which eventually turned into a repetetive clicking noise. I bought from a reputable volvo dealer, and now I'm wondering if they knew about it.
A good clue should have been that the car had 4 relatively new (but cheap) tires on it.

There's no way to predict when one might fail. They're either noisy or they're not. They'll usually make a clicking type noise when making sharp turns, like going in tight circles in a parking lot but when they're "toast", they can also be noisy going straight too.
A clicking noise on turns, accell/decell can also indicate worn driveshaft joints requiring a replacement driveshaft (front to rear). This is also becoming a more common failing part on XCs (new...about $850 for the part).
If you insist on buying an AWD XC, make sure that all tires are the same and that they're evenly worn and in good condition.

Personally, I never advise that anyone buy an XC as they have other issues too and are generally more expensive to own/maintain than the similar FWD V70 car.

A turbo FWD V70 will be more fun to drive, more power and far less problematic overall. If snow's an issue, get 4 good snow tires and you'll do just fine with it in winter.