I saw a lot of people having a problem with the sound in Predator Laptops running on Linux. My laptop is dual-booting on Manjaro and Windows 10.
Here's how I fixed my problem:
STEP 1- For Ubuntu users, open up the terminal and type this:
sudo apt-get install alsa-tools-gui
For Manjaro / Arch-Linux Users, open up your package manager (mine is Octopi) and search for alsa-utils and install it.
STEP 2-
Open up the terminal and run this:
hdajackretask
STEP 3-Select the codec, mine is Realtek ALC255.
Check the 'Show unconnected pins' option
Look out for Pin ID: 0x17 > select override > choose 'Internal Speaker(LFE)'
Look out for Pin ID: 0x1b > select override > choose 'Internal speaker(Back)'
STEP 4-You can choose to 'Apply Now' and test it (didn't work for me)
OR
Click on 'Install boot override' > Enter your password > Reboot
STEP 5-Speakers on both sides and subwoofer should work. It won't be as good as it is on Windows 10 but it is fine.
Here is a screenshot: 
I hope this helps someone else having this problem. Cheers!