After a while of light use, my i5 iMac will turn on its fan. It's not loud, but you can definitely hear it. Once the fan is on, it stays on, even if the CPU is under 5% load for 10 minutes straight. If I put it in sleep mode and wake it back up, the fan noise is gone again. Until it seemingly randomly decides to start up again. I've read about fan noise problems with the i7 under load, but not about i5 idle fan noise. Is this a thing? Can I do anything to prevent it?