Why is the fan on my mac book so loud

First, reset the SMC . If that doesn't do it, run the Apple Hardware Test to see if the temperature sensors are OK (run the extended test, and it will take awhile). If that's OK, bring up Activity Monitor (on your hard drive in applications/utilities) and see if any program is consistently running >30%. You can also linstall iStat Pro to see if high component temps are causing the fan to run.

I simply went to activity monitor and there was adobe resource synchronizer using 82% cpu i forced it to quit and fan shut down immediately. it was a relief, my fan had been running more and more frequently and at higher rpms for weeks now it seems to be back to normal

Thank you so much!! I had been living with that insane noise for the last few months and I did exactly what you said and it worked a charm!! 🙂

Excellent solution! Thank you!!

Thanks BGREG. same issue with the fan. With your indications i discovered dropbox was using the CPU over 50%. I closed Dropbox and the fan slowed down immediately. Thanks

I reset the SMC and it did the trick. Fantastic. The "Genius" at the Apple Store couldn't figure it out. Thank you BGreg!

as aboce noticed Drop box was using 97.5 % of my cpu (i7 )

and google chrome was using 27%

as soon as I ended these processes the mac ran quiet again

got rid of both