Here's a mod I've been using on private for some time and I would like to share.
Features
- Exterior and interior sound for gravel and grass (noticable mostly if you drive slowly).
- Interior and exterior sound of a mix of lovely SCREAMING truck gear axles and semitrailer tires.
- It does NOT replace any default or mod engine sound. It just adds background sound, so it should work with any truck, either vanilla or mod.
As a personal note, this gave me a new level of enjoyment on ETS2 because it ended that "muted" feeling when driving the truck. If you drive a lot in real life on highways as I do, you will understand what I mean (I love to open both driver and passenger window on tunnels to listen to trucks near me "screaming" 
)
Changes on 1.21:
- Included all the missing new sounds from 1.20-1.21 updates.
- Adjustements both to interior and exterior volumes and sounds, to try get rid of the "washing machine" sound.
Credits:
- SCS for sound files and main config.
- Ludmilla Power for interior cab sound file.
- Me (Irreo/Katixa) for parameters values, sound edit (pitch, volumes, noise, etc.)
NOTE:
I've been using this mod on private for some months, mainly because I didn't get a reply from "Ludmilla" after asking him for permission for using one file from a mod from him. I decided to publish this because I see there are lots of mods crediting him for cab sound, so I assumed he either doesn't care, or he didn't get the message. If you read this and don't agree, please reply and I will delete the upload.
Customization
If you don't like the volume on interior or exterior, feel free to edit the config files.
For exterior sound, adjust the volume parameter here:
/dev/vehicle/truck/common_sound_ext_data.sui
sound_noise_dаta: .asphnoise
For interior sound, adjust here:
/dev/vehicle/truck/common_sound_int_data.sui
sound_noise_dаta: .asphnoise
