Very loud noise on startup -- a PC problem solved
So, every time when we started our PC, we heard that the something starts giving a bad sound. After turning on, the computer keeps roaring like that for a while and after about 4-5 minutes the sounds go back to usual whirring sound (the "normal" sound that PCs make). As I know a louder than usual noise in your computer (or other strange noises), isn't something to ignore. These sounds are usually an indication that a fan is not working properly -- a potentially serious problem! I opened the PC carefully and found out that I was right -- it was the fan problem. It was already broken.
We took the PC to a fix computer store and the people there said the same -- the problem is the fan. I used the opportunity to let them clean the other fan, to change the broken fan and some other problems (USB, speakers). All this costs RMB 160 (~USD 24.19).
Now our PC looks and works like a new one!