Plinius 9200 - transformer buzz

I have a problem with my Plinius 9200. Buzz comming from it's transformer is occasionally very loud, annoying and distracting especially during low passages. It's not constant, for most of the time the transformer is silent. Have you experienced that with your Plinius? What could be the possibly reason and how to solve the problem. I've written to the manufacturer, to Plinius Audio but haven't received any answer.
Power supply 230V (Europe), dedicated PC (I have tried a couple of them on the amp).

Are you sharing power with your cable television? Also could be "Crappy Power" coming in from your local power company...I would at least make sure you have a dedicated line and go from there.........I have been there with the same issue and my situation isn't bad..Only during heavy power usuage...Hot Days ( high power use ) Cold winter days ( heavy Power usage )...I just have to live with it....Some days no noise other days " Modest noise "......I am also sure it could be other problems but thought I might bring my experiance to hopefully help.............
Thanks Thorman,
I do have a dedicated line and I didn't have the problem at the beginning. Now the buzz is more and more frequent.
Here's a quote from Roger A. Modjeski--who I figure should know a thing or two--posting on AudioCircle.

"One thing to keep in mind about toroids. If there is any DC on your power line the transformer will audibly buzz and the magnetizing current will go up. This is because they have no air gap. EI transformers have an unintentional air gap of about .001 inches. That's all it takes to keep a transformer happy with a volt or two on the line."
G'day JKuc
I have had exactly the same problem with my 9200. Plinius were great and exchanged my amp but i still have the same problem so it wasn't the amplifier.
I have noticed that my plasma tv which is plugged into the same power outlet makes my amp hum especially if the picture is bright ie lots of whites. Also my washing machine believe it or not as the motor starts and stops makes my amp hum in synch with the motor so i think its some sort of harmonics problem caused by the power supplies in the tv and washing machine.
I am concerned that this is causing my amp to run warmer than normal even at idle so i would also like to hear from anybody if they know what is causing this and if its doing any harm to my amplifier.

Thanks very much