Why is my iMac fan suddenly so loud? I have checked the Activity monitor and no applications are hoarding processing capacity. I have eliminated all automatic log in items in Preferences. Any suggestions?

Power or other problems related to unexpected system sleep, shutdown, lights or fans call for an SMC reset:

Resetting the SMC for Mac Pro, Intel-based iMac, Intel-based Mac mini, or Intel-based Xserve

1. Shut down the computer.
2. Unplug the computer's power cord.
3. Wait fifteen seconds.
4. Attach the computer's power cord.
5. Wait five seconds, then press the power button to turn on the computer.

Try Resetting the System Management Controller (SMC).

You're welcome.

Considering that I can't walk past an Apple Store without dropping $3000 who knows how much you saved.

😎

This thread started five years ago and is probably getting ignored by the experienced helpers here. Please start your own thread with a full description of you iMac from "About the Mac including sub-model (example: "Mid 2010 27-inch") and what macOS version it is running. DO NOT post the serial number for security reasons.

I tried this and it is still making noise. Help!

THANK YOU!!!

Thank you John. This worked perfectly.

It worked! Can't believe it. Thank you!

Suddenly after Hurricane Irma, my iMac's fan is running constantly....loud. I have reset as instructed now, twice in three days. Any other recommendations?