I went to C:\Users*****\AppData\Roaming\Microsoft Flight Simulator 2024\StreamedPackages & searched for ALL *.pck files. It found 40, so I deleted them all! I then exited the sim & reloaded. All sounds are back! 
I went to C:\Users*****\AppData\Roaming\Microsoft Flight Simulator 2024\StreamedPackages & searched for ALL *.pck files. It found 40, so I deleted them all! I then exited the sim & reloaded. All sounds are back!