Just reveived my CP4. What a stage piano. Delighted !

The mains power supply when power on, and during a good half an hour, makes a high pitched noise. I wonder if other owners of the CP4 have noticed it.
It is true that you can only hear it if you put your head closer to the right side of the keyboard - keys and open back ventilator grid -, but nevertheless it is there and it is quite a thin high pitch and very uncomfortable noise.

I have the CP4 connected to a Belkin power surge 6 sockets unit to prevent power spikes.

P.S. Forgot to mention: it is indifferent having the CP4 connected only with the main power cable (without speakers or other devices connected to it), connecting it to other wall socket or removing the multi-socket power surge. The high pitch hiss is always there. The strange thing is that after 1 hour or so, the noise is almost gone. Does the internal transformer makes less noise when hot?... Any reason to replace the CP4? Would appreciate any help.