The driveshaft is sometimes called a "propeller shaft".  There are very few problems relating to the driveshaft itself.  The Mazda factory service manual warns of balancing washers on the bolts that secure the driveshaft to the pinion flange going into the rear diff, but we've never see such washers.  The driveshafts are balanced themselves; you'll see "patches" of metal welded on various areas along the main shaft.  This would eliminate the need to balance the driveshaft externally.

Typically, U-joints go bad that produce rythmic noises which increase with vehicle speed.  If these noises are coming directly under the car, it could be a failing U-joint.   The driveshaft can be removed, and the U-joints easily inspected thereafter.
FC3S Pro:  Problems, Components - Driveshaft, Universal Joints

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