Issue can be tested without a Headlessclient. Only a dedicated server is required, which can be hosted locally or remotely.
But because the rainParams command is empty on anything dedicated I decided to include it in the repro steps.

1. Start up an dedicated server running any test mission where you have access to console and watch fields.
2. Check the rainParams on the client side and see the array filled with data.
3. Global execute diag_log rainParams and check server/headlessclient log to see an empty array being returned.
4. Server execute overcast and rain commands to make it rain: 0 setOvercast 1; 0 setRain 1; forceWeatherChange;.
5. Server execute setRain with different rainParams, example setRain ["a3\data_f\rainnormal_ca.paa",4,0.01,15,0.05,25,0.2,0.02,0.02,0.8,[0.101961,0.101961,0.101961,0.14902],0.1,0.1,0.5,0.3,true,false]; <- changes the new snow option to true, which makes the rain make no sound.
6. See no effect happening on client side. rainParams command doesn't change either on client, and on server/headlessclient it's still empty.
7. Global execute (or Local execute, just make sure the client runs it) command from step 5.
8. See changes happening on client (rain sound stopped), including a change in rainParams on client side. Server/headlessclient side still empty array.

Happens both on Linux and Windows server builds.
Tested on Stable, Perf and Dev branches.

Can provide more repro (mission) or information if required.