There could be several explanations that are consistent with the cause of the noise being mechanical hum and it only appearing on your latest 200 and not your earlier PJs. First is that your power company is doing something different and whatever this is has introduced DC current on the AC line. Another explanation is that Sony is now using new power supplies and these are more prone to hum. Another explanation is that the particular PSU that is in your projector may have had less varnish or super glue applied (or maybe it was improperly applied) to the laminations in the PSU.
The sound would likely vary. From the link:
If you suffer from this noise problem, you've probably also noticed that it's intensity varies depending on the time of day, sometimes even the time of month. The reason it varies is due, in large part, to the quality of the AC line voltage and how much DC is on it.
I hope that the new PSU fixes the issue for you. If not, try the Humbuster product. It is a risk-free trial.
I have no connection at all to the company and have never even used any of their products. I have been told by others who do know that they very well.