Buzzing sound from NAD 3155

[Danieluh]

Hi
I have a NAD 3155 that sends a 50-hertz sound to the speakers og headset.
The components looks visually ok, and the entery-voltage to the mainboard looks ok.
Where should I start? Where is the problem most likely?

Here's the schematics: https://dl.dropbox.com/u/463435/nad_3155_schematic.pdf


Thanks for every serious reply.

 

[JonSnell Electronic]

Is that at power up only or all of the time?

 

[Danieluh]

All the time after it's powered up.

 

[amptech]

Check your preamp supply filter caps