Grinding noise start up for 15-20 minutes

[Zinnia2020]

Pavillion has always been a bit noisy. Last four times, grinding noise when boots up after power off or first thing in morning after on all night. If I disconnect power cord and plug in, then don't get noise. Diagnostics says "no fan." Have checked CPU use (fine) and also disabled most programs at start up. Vacuumed air vents. All in one is two years old. What to do?

[WAWood]

@Zinnia2020 

The grinding noise, coupled with the fan notice, tends to indicate that your fan is failing -- and that is a serious issue, as that will cause your All-in-One to seriously overheat and shut down.

HP does not make these easy to open and fix, and you would need to take this to a local computer repair facility that can open the case and replace the fan for you -- if you can find any that are open these days.

Good Luck

[Zinnia2020]

The fan was my first thought, too. But I don't get the noise if I pull out power cord and reboot.

I only get the noise if I start up after an 8+ hour hibernation or turn off computer and restart without pulling out the power cord. 

[WAWood]

@Zinnia2020 

OK, but there is a strong possibility that when running on battery, you have a power plan being enforced that throttles the CPU and this would cause the fan to run a lot slower, possibly being inaudiblt.

To check this, when on battery, try doing stuff that will tax the CPU like playing a video or surfing the net jumping from site to site.  See if that speeds up the fan and causes the noise to restart.

The other "moving part" is the hard disk, but that would be the same, and make the same noise, whether on A/C power or the battery.