Not So "White" Noise

Since we moved into our new 2 bedroom apartment to prepare for little man's arrival, we have almost constantly heard music playing, well not necessarily the music. We can't hear the words or the tone all we can hear is the bass and it sounds like the same song, over and over and over . We can only hear it when we are in our apartment, once we step out and close the door it's gone. The other day we went and knocked on the apt door across from us since he seemed like the only one listening to music at the time. He turned his music down and it seemed to stop so we thought "ok problem solved" Well it's back and he is not even listening to music tonight. I first put my ear up to the door before knocking to talk to him, no music. Once he answered no music. So obviously it's not him causing this problem day after day, night after night. The way our apartment is layed out is consisted of one building two entrances, eight units to each entry. Four upstairs, Four downstairs. So tonight I ventured out (once again, since I did this about a week ago as well) Listened to everyones door in our entrance. No one was listening to music but I knocked anyway. 3 out of 4 neighbors downstairs are elderly, only one was a young couple who had guests over, including kids and did not even have their T.V on at the time. They talked to me for about 10 minutes and I was reassured I am not the only one being driven crazy by this beat. She has heard it during the day. My neighbors upstairs are not the culprits either. I have not yet ventured over to the other entry in our building to listen to the other 8 neighbors in our building, but plan on doing so tomorrow. Am I crazy? Is it hormones that is making it impossible for me to get over this noise? Or am I just preparing to join the mommy club? If this noise is going to be waking up my newborn I will have to shoot someone (not really but Ken does have a paintball gun and/or airsoft gun that I know how to use). I want it to stop. Unfortunately I can't get it to until I find our where it is coming from. Wish me luck as I spend my day off tomorrow trying to find the not so "white noise" culprit.