McIntosh preamp C504 output noise& 8207;

Good day, I received recently Mcintosh pre amp C504 (1984 production year). All seems to be fine, except I can hear contant noise from output. Pre amp and amp are grounded, connection is good and even if volume is completly down there is quite noticable noise from this preamp. Easly to hear from quite few feets away. This noise get intensify if I put volume or 10KHz up.

As spec says 100db noise ration I would imagine in properly working unit this noise should not happen (as it does not happen in many other pre amps). So my conclusion is, there is something wrong with this particular unit? What do you think?

Thanks for help
Could be a power supply taking a digger. Also before you send it off to a repair shop try plugging it in to a differnt outlet. Also try reversing the polarity on the plug since it doesn't have a 3 prong plug. And one other thing you may try is run a ground wire from the chassis to the center screw on your wall outlet plate.
Theo, I tried all that and did not work. Noise it not typical hum, but rather higher frequencies based. I think its time to see a technician and fixed it and probably refresh few other elements. Thanks for help, nsnotes