Just an idea as I noticed that in case of different sounds possibilities on your PC .... Assetto Corsa doesn't have the possibility to automatically choose the one you actually use.
( in my own case: 2 screens with possible sounds, 1 headphone Logitech Wireless on G Hub and 1 Sennheizer using Realtek audio ).
Go on track and find in the menu at the right the Sounds App Icon and click it.
Check if AC sound option is matching you actual sound system.
In the negative, choose the right one and restart AC .... you'll have sounds afterwards.