BY FAR it's most likely either the hard drive or a fan. There is almost
zero chance that it's the LCD inverter or either of the other TWO
switching power supplies inside the laptop (the main power supply, or
the CPU Vcore power supply).

Also, FWIW, the voltage on the lamps is probably quite a bit lower then
your figures .... probably more like 600 to 800 volts (higher
momentarily to start).


Davy wrote:
> Best trying to determine if it come's from the speakers, electronic
> or if a mechanical noise, hard drives can cause this problem and so
> can CD ROMs.
>
> I have known switch-mode power supplies cause this..... and there's
> one right inside - the inverter for the backlights, this little
> device steps the 12V dc up to around 1,800V, just wondering if it's
> something arching over on the HV side, whether this would affect the
> light from the CCFL's would depend on the nature and severity of the
> fault.
>
> Once the lamps have ignited the running voltage drops to around
> 1,400V.
>
>
> In tv's and videos I have used a length of plastic tubing as a
> stethoscope to locate the area and usually locates the component or
> mechanical gear wheel.
>
> Davy
>