It all happened in one split second. I was on a bad site. I caught a virus. *censored* broke loose, my android tablet started making repetitive notification sounds. My HP desktop computer REBOOTED and a dos screen SAID one of my hard disk's (i have 3 internal 2tbs) faillure was imminent, i should start backing up soon...
I tried reinstalling windows 7 a few time, then windows 8, it worked but a strange noise appeared, its like a fan that seems to want to start something but just gives up after a second. Its not that loud but it not steady, it goes up, then goes down, in a vicious circle. So i find it annoying.
I dont have a microphone to make you listen... im sorry.
Do you know what if could be?
Could a software resolve the issue?
I scanned the hard disks for errors and the results say they are fine.
Could a virus do such a thing even after a few formattations of the drive containing windows.A virus cannot do this...so No.
A coincidence at best.
If the HDD's checked out fine it's something else...
Software will not resolve the issue.

You will need to remove a side panel and isolate where the noise is coming from...
If the PC is over a year OLD it may just need general physical maintenence and a cleanout...grab a can of compressed air and blow everything out...when blasting the fans hold the blades in place with a Q-tip or pencil...

Report back with the results... Paranoia.
 Fluke.
 Unplug the fan. 
 Also check the PSU (Power Supply UNIT) fan and casing fan (if any).