I checked the pls-330 supply on the web.
Indeed two fairly large toroidal transformers are used for the left and right analog power supplies.
If you know what you are doing and use great caution (I don't want fellow forum members to die because of my instructions) you could lift the cover and very carefully run the unit while the power supply is open.
If that made it louder you could investigate isolating the cover with some dampening sheets.
Also if you put some controlled pressure on the transformer it can become less or more.
By all means if you are not comfortable ask a service guy to invest the root cause.
Good luck
Peter
|