[SOLVED] What is the clicking noise when PC goes to sleep?

[seagatedoge]

I have wondered what the singular click noise is when the computer goes into sleep mode. First I click 'Sleep', then the screen goes dark and finally a physical click before it enters sleep state. The click is also present when woken. It's not a problem as far as I know. Just curiosity about what is happening.

 

[Aeacus]

On top of my head, it could be 2 things:

1. HDD read arm positions itself to non-operational position (off the drive platters) and does that with audible click. Same click can be heard when it returns into operational position (on the drive platters).
2. PSU's mechanical relay switch turns PSU off when PC is put to sleep. And when PC is awakened, same switch turns PSU back on with audible click. Some PSUs can have that "click" quite audible.

 

[Grobe]

It's the read/write head of the harddrive that lands on outer position when powered off or (my assumption) in power saving mode too.

 

[seagatedoge]

Thanks for the replies. I think it is the PSU then, because my PC only has solid state drives.