try putting the suspect tender on the track without the locomotive in front of it. apply track power and see if you hear any background sounds. if yes, the previous owner intentionally or inadvertently used the blend feature and turned the background sounds down all the way off.
I tried that in conventional and nothing happened, however, I still can activate the bell and whistle from the transformer. Also Rudy, every now and then while running the loco in legacy mode, you’ll hear a quick burst of chugging followed by silence.