The sound that you hear could be from a misaligned carrier bearing. This is the bearing that helps support the CV axle on the passenger side of the car. I purchased my Fiesta new and it did not have this sound until after my throwout bearing was replaced (actually, after the throwout bearing was replaced a second time). During the replacement of a throwout bearing assembly, both of the CV axles are removed so that the transaxle can be removed from the car and then reinstalled after the transaxle is bolted back onto the engine. Because the dealer damaged one of the CV joints during the throwout bearing replacement, I ended up replacing both CV axle assemblies. The new passenger side CV axle assembly came with a new carrier bearing. Once I replaced the CV axles, the whine went away. Therefore, I'm pretty sure that the whine that I was hearing after the throwout bearing replacement was caused by the dealer improperly mounting the carrier bearing.
A possible reason that so many manual transmission Fiesta owners have the whine is that aligning the carrier bearing is a little tricky. The outer side of the outer race is rounded. This keeps the axle from moving in the lateral direction. However, the carrier bearing does not self-align very well during the mounting process. To attach the bearing to the mount, you need to carefully seat the bearing and wiggle it back and forth until you feel that it is properly centered. Once it is centered, you then need to attach a new bearing strap (and carrier bearing shield, if you car has one) and put both nuts on the threaded studs that hold the strap (and shield) on without moving the bearing. Again, you need to keep the bearing in firm contact with the bearing mount during the assembly process. You then need to tighten the nuts about an 1/8 of a turn at a time, going from one nut to the other a few times, before using a torque wrench to get the proper torque. Since the bearing strap will permanently deform during the tightening process, it cannot be reused. If the bearing is not perfectly centered when the strap is tightened, the bearing will be cocked a little, which will cause the balls to ride on the edge of the races, instead of the center.