There is a strange noise coming from the back of my PC case. At first I paid no attention to it, but when it kept on being even louder I realized that something must be wrong. I just don’t know what. I haven’t installed any new hardware. But I remember that I once opened it in order to clean the dust.
I think that the noise is caused by a cooler or vent for processor or motherboard. Sometimes some of the wires and cables that are inside of the case move slightly and the fan is brushing against them thus causing a strange noise. Or maybe the dust that you wanted to clean got in the fan and started making the noise. I suggest you to check whether the coolers and vents are working properly. Go in BIOS and see how many rotations per minute your coolers have. If it is under a certain value or if there is something wrong you will be able to see it there. Maybe you just should have your PC case cleaned.