How to stop night time barking at apartment noises?

I rescued my 2.5 yer old pit bull terrier about a month ago from a shelter- for the first month she didn't bark very much at all- except when someone was directly at my door. This week she has started to bark at night at some new noise in our apartment building that I can't identify beyond it being a loud Bang that almost sounds like someone is dropping furniture (it's very inconsistent and intermittent and I am also not sure on where exactly is coming from upstairs) but now she is barking in the middle of the night at it. I do my best not to overreact or speak loudly so she doesn't think it's disturbing me also but I am just anticipating complaints from my neighbors about her barking and I need some help figuring out how to curb this behavior. Here's what I am already doing: white noise is playing (it doesn't drown out the sounds), calming music is also playing to try and relax her. When she does bark I pet her to calm her down (but I'm not sure this is encouraging the behavior- I can't let her just bark it out though in the middle of the night). I've tried to do a "speak" "quiet" command but she doesn't bark on command- however when she is quiet I tell her she's a good girl. Any advice on other training techniques or ways to react to this would be very helpful- I think both of us and my neighbors would appreciate undisturbed sleep. Thanks!