Sudden Loud Fan Noise

[Malivar]

Today, I got home and turned on my iMac 21.5 inch. On a typical day, I'd here the "BONG" and then everything would be normal. Today, my fans, or something inside the computer, sounded like it was going crazy. I have no idea what's wrong.

Anyone have any ideas how to resolve this?

 

[jampat]

How long did the fan stay high? Did the computer eventually boot? Sometimes while installing updates, the fan will run at full speed while the update happens.

 

[Malivar]

How long did the fan stay high? Did the computer eventually boot? Sometimes while installing updates, the fan will run at full speed while the update happens.

I'm on the computer right now to see if the fans quiet down... Nothing yet. The fans are STILL high. Hasn't booted, and I installed the new update like, 5 days ago.

 

[JasonR]

My 27" iMac fans revved up really high while doing a system update (I believe it updated the firmware). Shocked me for a second.

 

[FarSeide]

Run AHT that came with your computer. High Fans often equals one of the sensor gone bad and there are many sensors on the MLB.