Jay's Audio CDT2 MK3 hum

@cleeds : Here in Poland +/- 10% is allowed, so up to 253V is "OK". Technicians were called, checked the voltage and confirmed the problem is with excessive local production by PV installations. Power lines will need to be replaced which will not happen any time soon. In case of any damages excessive voltage can make, they pay for repair. I'm monitoring my installation with Supla system and Zamel monitors and all the anomalies are recorded.

@tonnesen My installation consists of two strings, 6 + 4 kWp, oriented east-west. Fronius inverter I have, stops working in case of 254V+ measured in any phase constantly for a few minutes, then checks back and if voltage dropped, starts again. The inverter stops working and not individual panels or strings of panels. Your installation must be different. Sure there will be more problems if more installations will be connected, here and where you live, if no new lines and perhaps auto transformers will be installed in the local network. 

No hum at night when voltage drops to 230V or below.

@baylinor I have a written warranty from a local-private importer so it is not that I am not covered. Starting this discussion I just wanted to be better prepared with my claim. If I get any responses from the members (especially from EU) that the transport is DEAD quiet (in the casing) at any excessive voltages, it will be strong indication that my unit needs repair. Another possibility is that all units slightly hum but their users are not bothered... Funny is that the Berkeley Audio Design HDCD DAC of the importer hums like hell (by my standards at least), but he likes it so much so ignores the noise. "Unfortunately" at his place voltage is dead stable so my problem could not be replicated. 

You said "no clue what EU power units may sound like" but I don't hear the power unit which is on the left side but something buzzing at the right side. Is there anything that could vibrate there resulting in 300Hz noise?

Thanks all for the comments.

@knock1 Thanks for confirming yours Jay's is totally silent. Are you from Europe? Have you measured your voltage? 

"I would think that such a high voltage might cause the hum": If this is normal situation with CDT2 MK3 EU version, it is quite disappointing. None of my other old and new EU made pieces seem sensitive to the voltage anomalies. ZERO hum even at 260V. The simplest test to see whether it is some design flaw or a problem specific to my unit, would be to borrow another Jay's and compare them side by side at my place. Not impossible.

@creativepart Thanks for confirming your Jay's is silent. I have my $80 power "regenerator" keeping my voltage at 228-232 V and it fixes the problem. Not the most elegant way, though.

@baylinor I don't want to break the seal on it to eventually lost warranty. Whatever it is worth... Would like to leave it to my importer but the problem is his voltage is stable and nothing buzzes at his place.

@knock1 Hi Tomasz! So you must have Polish roots :)

Been traveling a bit but finally got the transport to the seller. He's borrowed an autotransformer to play with higher voltages than nominal and confirmed my observations. He's found that once the top lid is off there is no hum audible. He experimented a bit with the transformers, which don't produce any audible sound when the lid is off. With the lid on the screws needed loosening to silence the hum. So, the whole thing that bothered me whole summer is the transport housing resonance amplifying otherwise inaudible vibrations of the transformers. Hell knows why it is the strongest on the right side. I am relieved that it is only a mechanical "issue" and nothing wrong in the electronics. Although I fixed it by using a cheap voltage stabilizer, I might try to put some  anti-vibration insulators under the trafos, So there would be no rigid connection between the transformers and the transport housing. 

Again, thanks for all the comments.