Thanks for the reply. The noise is constant, it occurs whenever the backlight is not running at maximum (after changing brightness using the nVidia driver). I do not experience this with Windows or when I switch in VT. I'm going to round up some t510 users in other forums to confirm this. I hope that the nvidia driver is only using non-optimal brightness graduations or "steps". It sure would suck if this was some sort of complicated issue with the backlight resonating with the LCD when using certain timings
. It is an LED backlight though, so I bet this is less likely than it would be with CFL.
edit: I added this xorg.conf stuff to ThinkWiki (a Linux wiki for ThinkPad Users). Users have already posted comments that confirm this issue.