That really depends on the age of the house and the conditions of the flooring.  I have been in houses primarily older ones that had floor boards that were far from uniformly jammed together without any additional covering over the top.  I've also been in houses that were undergoing a remodel or work on the floor above and it was very clear what was happening below.  (It could have been happening here we don't know.)

The other thing is they could have said we won't go past X line... anything that comes from beyond it is hostile.  Though that usually happens more in the military than in the police force.