Ever since the most recent RageMP update, I know that a lot of people have been having issues with interior music, car radios being too loud and etc.
Turns out, there is a fix for this, and it's quite simple.
Load directly into GTA Online from your GTA V menu (do NOT go into single player first, but load directly into GTAO).
Go to Settings > Audio > Move the Music slider to 0 and close the menu.
Open the original menu and go to Online and then Exit Game from