My neighbors keep complaining, but we're quiet!?

[frostbitten]

My fiance and I have lived in this apartment for over 8 years and have never had an issue like this before, in fact it's quite the opposite of what I've heard about! Our neighbors moved in a month ago, they had to move from their apartment (they lived there for 8 years too with no complaints against them) due to some water damage and moved below us. We play our music, but we don't play it loudly at all, nor do we play our TV loudly. Repeatedly, they bang on their ceiling and come knocking on our door telling us to turn our music or TV down, but if you go downstairs into the stairwell, you can't even hear it! We play our music in the living room and both work evening jobs, so we're up fairly late. We asked them if they slept in the living room and they said yes, which explains why they're evidently so sensitive, but it's getting to the point now where it's just downright ridiculous.. We called the cops and had them come talk to us, because we were frustrated and even talked to the rental office about it! The neighbors below us are just too sensitive or something! They complain that we will wake their newborn son, but we try to explain..we live in an apartment, you have to expect SOME noise, right? What should we do? This keeps happening and there seems to be no solution. We've gotten to where we can't even relax in our own home due to these idiots below us. (I also am aware of the 11pm-7pm noise ordinance and we are within the boundaries as well.) Advice is definitely appreciated, here!