If the unit you had installed is a refurbished one, then it would have been fitted with new regulator, problem is that some firms get the cheapest parts they can rather the use quality parts from reputable manufacturers.
Unfortunately thats not always the case these days, its al to common for some to simply replace the faulty parts, clean them up and sell them on. Reality is that teh regulators are pretty bomb proof, its the bearings that tend to go noisey....
If you have the reciept for the original work it might be worth persuing a warranty claim.
Mark, 'refurbished' usually means unit cleaned and re-greased with a touch of graphite grease, the bearing replaced, regulator replaced, coils tested and repaired if broken, then unit tested to manufacturer’s specifications.
Simply replacing a bearing means the unit has been repaired, but such unit should not be sold as ‘refurbished’.
However the problem with refurbishing that that many firms throw-away the original Bosch/Lucas/Magneti Marelli etc regulator – which may be perfectly good – and replace it with a cheap east-European unit thus actually degrading the long-term reliability of the alternator.
The warranty claim might be in order though....