Check setting 43, "background music volume". Move towards 01 (loudest, and default on a factory reset).

Lower numbers are louder.

The only other thing you might try out of desperation, is a full on factory reset of *all* settings. From my observations on other threads, occasionally a factory reset fixes "odd stuff" including sound. Stuff that you'd think would otherwise be fixed on a single setting basis. If you're about to send the board off, it might be worth the try. You'll of course lose the high scores in the process, but if you're sending the board off..

I am studying the schematic.... not the best at sound stuff, but i don't see a place where they mix two different analogue sound inputs like one is music one is effects.

There is a DAC that feeds a left and right channel. Two channels are mixed together for mono sound. Then there is a two 2030amps (push pull circuit???). I don't think this is going to be in the analogue / amplification side.

The digital side i have no idea how the XILINX sound chip works so i get stopped there. It is a 100 pin SMT, so not really easy to just swap in a new one.

Monopoly used the BSMT2000 (customized TI DSP) chip from the factory and not the XILINX processor. Of course finding a replacement to pop in there is nearly impossible.

The sound section on the WS board is the same as DE stereo sound. One of the things this means is that there is no validity checking on the ROMs:

https://pinside.com/pinball/forum/topic/help-request-vnd-voice-rom-2-sound#post-2525563

Could have another bad ROM or bad socket.

You can also swap CPU chips on the board and see if that has an effect.

Full reset is a good idea as well.

viperrwk