New Toshiba monitor Whining 15khz

My trisync monitor which I bought last week as brand new is producing a high-pitched whine at 15khz which is the same sound as when nothing is connected to the monitor (the no-signal screen). It has always produced this sound but I'm wondering if there is something wrong. Anyone else had this?

Since the monitor is designed for sega hardware and therefore will only accept 0.7v p-p RGB levels through its d-sub 15 pin vga connector I am having to run the jamma connector through my XRGB2 before plugging it into the monitor. I'm just wondering whether I'm losing picture quality by running it through the CRGB first and whether it would be better to make a custom jamma-vga harness with resistors to drop the rgb levels.

FYI the picture looks fine at 15khz using the XRGB2.

Doesn't it have a switch for changing the impedence from 1kohm (VGA) to 75ohm (15khz RGB)?

Whenever I read Monitor whine I think of:

http://homearcade.org/BBBB/whiny.html

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Monitor/Video Forum
http://forum.arcadecontrols.com

I have seen a switch on the monitor but I have no idea what it does and therefore don't really want to touch it...

also I'm already inputting 0.8v (p-p) RGB and 75ohm sync so in theory it should be fine. It's just at 31khz there's no sound whereas at 15khz there a high-pitched squeal - just wanted to know if that's normal or not...