Very high fan speed on Ubuntu 18.04

I struggled with fan speed and thermal issues for a long time before I found tlp which has solved all my problems. You can learn more here:

TLP brings you the benefits of advanced power management for Linux
without the need to understand every technical detail. TLP comes with
a default configuration already optimized for battery life, so you may
just install and forget it. Nevertheless TLP is highly customizable to
fulfill your specific requirements.

Installation is the predictable

sudo apt install tlp

Configuration is automatic and I’ve never had to change it out of the box.

If tlp by itself doesn’t solve all your thermal issues there are specific steps you can take for ASUS Laptops:

Kernel modules overview

• asus-nb-wmi is a kernel module, which is included in mainstream Linux kernel and is loaded automatically in Asus laptops. It will only allow to control a single fan and if there is a second fan - you will not have any controls over it. Blacklisting this module will prevent keyboard backlight to work.
• asus_fan is a kernel module, which allows to control both fans on some older Asus laptops. Does not work with the most recent models.

For myself after installing tlp I was able to remove a couple of fan control programs I had struggled to setup for my laptop. However I do not have an ASUS so you might need something more than just tlp.