那个据说是热胀冷缩，并不是真的有东西掉。
楼上开门关门走路到真没听说过。

公寓house rule对nuisance是有定义的。
In order to preserve a pleasant living environment, please give consideration to your neighbors by not extending noisy activities or engaging in offensive conduct such as the playing of musical instruments, television, karaoke, stereo equipment, mahjong, or other noisy pastimes, etc., into the late hours of the night (after 11.00pm), early morning (before 9.00am) or during the festive season.
楼主并没有做错什么，所以对抗方式来投诉，楼下过分了。
从调节处理方式的来说，楼下起码应该亲自去商量沟通，就像某位层主说的送个水果聊聊。承认是自己对声音敏感，互相体谅一下。只要楼上有诚意尽量避免，诚意到了就可以了。
长久来说，不考虑卖房，楼下可以考虑装修吊顶，几年做一层隔音棉。毕竟对声音敏感更多是自己的问题。楼上有小孩，起来喂奶还要为了照顾楼下而去客厅，已经是相当谅解合作的态度了。

多说一点，物业和警察对这种问题也只能调节，没有什么别的办法。