Laptop squeals and does not boot to Win7

Vexing hardware issue - any thoughts appreciated.

Trouble-shooting my daughter's HP G62-435DX lappy. Its been a faithful tool and adequately serves her needs but has recently started making a high-pitched near constant sound just as it boots into Windows. The sound emanates from about where the speaker is - which does not correlate to where the cpu fan, HDD or RAM is located. At this point the cursor blinks in the top left corner of the screen, the noise continues ... until a hard power off.

Sometimes, after 30-60 seconds it will boot through to windows, and at that point it operates normally until shut down - however long that is. If I boot from CD with Partition Wizard and then select boot from hard drive instead of PW, it is fine and operates normally.

I have blown the dust-bunnies out and run a few diagnostics - everything checks out OK. Speccy says mobo temps are fine (53º-65º), the HDD has no errors, and I hear the fans spool up when the cpu goes under load. The BIOS is up to date. HD diagnostics says battery is OK and it still charges to 90+%.

At first I thought maybe the screen inverter or power supply (there are scads of forum posts on high-pitched laptop noises), but it happens with or without battery and the screen brightness is undiminished.

So it seems as though - as long as it boots, everything is good. Could this indicate a failing hardware component triggering a sensor? If so, what? But then why does it run just as always once it completes the boot?

Any ideas much appreciated.

Yep - been through that. It always runs Avast (and its behind a router) - comes up clean.

Computer0304 said:

Try running Malwarebytes : Thank you for download Malwarebytes Anti-Malware. Remember to uncheck starting a free trial. (If that still exists)

Full scans in both Malwarebytes and Avast show no issues.

Britton30 said:

It could still be a fan going bad which runs faster during the boot process and slows in Windows. Most CPUs and GPUs run a bit hotter at boot than after booting is done. The location of the whine may be falsely located due to vents and internal baffles.

It could also be the internal power converter with a bad coil, or the inverter.

It is very quiet at boot (an early thought was the CPU fan was NOT starting and the sound was a warning alert) but when it does boot, I can immediately hear the fan increase speed and feel air blowing out.

With the back access panels removed, I held the laptop up to my ear to better understand where the source.

This laptop has an external power supply.

Computer0304 said:

It may be the PSU making the noises. (If laptops have one which I think they do) The only solution if it is the PSU is to get a new laptop unless you find a way to replace it.

The power supply is external. And would not explain why it runs fine once it makes it through the startup sequence to boot the OS.