The fan on my Mid 2017 Mac Book Air was constantly running. I tried several things before finding a fix
Remove Browser Extensions
Shut down All 3rd Party Apps / Menu Bar App that were running
Scour Activity Monitor for any unusual activity
After searching the forums I came upon a post about Energy Savings Pref - and it hit me like a bolt of lightening - I changed the Energy Savings Preferences from On Battery - Uncheck - Put Hard Disk to Sleep
I went into the ES Pref and Checked Put Hard Disk to Sleep on both Battery / Powered Settings - and low and behold - NO MORE SPINNING FAN !
I hope this help others in their quest to quiet their MacBook !!!