We have a new construction home 7 months old. In the past 3-4 months I have noticed a bounce in every room of the house. The TV rattles in the entertainment center and the dishes on the table rattle when walking in the kitchen. Same thing in our master bedroom, everything rattles when walking across floor. We have engineered I joists 12 in spaced 16 in apart. The span the I joists cover is 21 feet. Is this normal? We also have one joist splitting and our builder won't come look at this problem. If builder isn't responsible, how do we fix it?