What is considered unreasonable noise in a condo? When is the complaint unreasonable.

We did not have any problems living in our condo before my husband and I had our 3rd child . My downstair neighbor has been banging on my floor ever since my child started walking ( now 2 1/2). On 2 occassions now (11 am and 6:30pm)my neighbor came to yell at me and following the 2nd time w/ a letter saying that she thought "i made myself clear,I am not going to live listening to your kids,that I can hear your doorbell , your alarm clock, your smoke detector, your answering machine . You have a loft, if your children has to jump make them jump there! (should I carry my child all the time?). So we moved to the loft, but then they banged again while we were watching TV in the loft then called saying they could hear a noise like paper shredder. No footstep. We don't know what to do.