I have a PC I built myself and up till the last couple of weeks, it ran pretty quietly. Now I notice that after I wake my computer up from sleep mode, one of the fans in the back (don't know if it's the case fan or the PSU fan) comes on and sounds like it's on high. The sound isn't strange in the sense that it sounds like a normal fan, but a fan that is running fast with a shhhhhh sound of air being pushed or blown.
This sound will continue until I restart the machine ... mostly. Sometimes it continues even after that mostly it will go back to a normal quiet state. This issue doesn't happen all the time, just sometimes. In fact, most of the time it doesn't happen.
My concern is that one of my fans is on it's way out. But since the problem isn't consistent (i.e. I never know when it will happen and when it won't), how do I diagnose and/or fix the problem? How do I determine which fan it is? Or should I just swap out my case fan and see what happens?