I hear screeching sound coming from my PC, a self build system. The workaround? Just kick the case a bit (pressing on the case seems to work too, but sometimes it seems to be triggered by stepping on the case too ... when I use the case as a leg rest lol). I thought it was some wire touching the fan, but opening the case, it does not seem to be so. What might be the problem?
CoolerMaster Elite 335
Intel Core i3 2100
ATI HD5670 (not sure what brand exactly, but probably ASUS)
8GB Kingston DDR3 (2x4GB)
Make sure the optical drive and HDD is secure in the slots. I had the same problem too, and pushing down on the case would fix it for awhile. I made sure the HDD was secure and it eventually went away.