Alternative solution.
If you have as hard of a floor as it sounds like you do, place some large speakers facing down directly onto the floor. Play Yoko Ono songs 24/7 for a week at a high volume (it's highly suggested that you take a vacation during this time). When you return, you'll find that the noises from below have magically stopped (plus you'll have more space which can maybe be used as a studio?).
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Paulo beat me to it. ?
Of course, since this is the Coffee House, just editing your thread to say something like "This post intentionally left blank." works as well! ?
What about covering your floor with a nice rug? I'm not talking about something permanent, just something to see if that really helps. As Bruno said, the way apartments are designed might be your biggest issue.
As a previous third-party FBA seller, I can tell you that we received a LOT of returns that were completely new and unopened. That said, it's part of the reason we closed that business, yet it's part of the Amazon model. So, obviously that means you can try one of those items and simply return it yourself if it doesn't work!