Found the source of the problem.
I've got the threat warning volume knob bound to a potentiometer in my simpit. As soon as I cleared the axis binding in the controls the RWR warning sound started to work as expected.
@NineLine I'm not sure if this problem is caused by my setup or if a bug crept in here. Before the latest updates it worked flawlessly. Maybe you can check it out and see if the problem is on your side. Do you still think this thread should be flagged as "user mods"?
Thanks for your work! Appreciate it, keep it up!