I believe you are allowed to sing in your own home without worrying who is listening outside. That would be a d’eved on their part. At any rate YOU are allowed to sing, the onus is on men who are not allowed to listen to you. So if they don’t come knocking on your door asking to come in and listen to you then there should not be a problem. If they don’t put their ears to the floor to hear you more clearly that should not be a problem either. Whatever they do hear is distorted and filtered through the floors, walls, insulation, etc.
Ask your Rav for peace of mind and then enjoy yourself. May your tefilos reach Hashem through your voice in song.