There are several things that might cause fans spinning at high speed: - Some application is using a lot of CPUs and other resources - Spotlight is indexing t

There are several things that might cause fans spinning at high speed: - Some application is using a lot of CPUs and other resources - Spotlight is indexing the hard drive, and is misbehaving (see for mdworker processes) - The ventilation holes are physically blocked or there is a lots of dust - The System Management Controller is misbehaving (especially on some 2013 and 2018 and later MacBooks which have T2 security chip). Resetting the SMC often helps with strange hardware problems. Apple support links: * [If the fans in your Mac run at full speed when you turn it on - Apple Support](https://support.apple.com/en-us/HT204463 https://support.apple.com/en-us/HT204463) * [See how apps affect Mac performance, battery runtime, temperature, and fan activity - Apple Support](https://support.apple.com/en-us/HT203184 https://support.apple.com/en-us/HT203184) * [Keep your Mac notebook within acceptable operating temperatures - Apple Support](https://support.apple.com/en-us/HT201640 https://support.apple.com/en-us/HT201640) * [How to reset the SMC of your Mac - Apple Support](https://support.apple.com/en-us/HT201295 https://support.apple.com/en-us/HT201295)