I did install underlayment underneath the laminate.
I did leave a 1/4 to 3/8 inch gap in most places around the perimeter. If there are some areas that are closer than that (such as near a floor track for a closet door), will this be a problem?
I think the noise problem is that I nailed the quarter round on an angle which meant the nails ended up near the bottom of the baseboard molding, which may have caused some tension on the boards or some unwanted noise between the boards and the quarter round. I'm not sure, but when I removed some molding a re-nailed it straight in (parallel to the floor) things quieted down quite a bit.
I'm not too concerned about the closet anyway and you are probably right regarding the echoing. After shelving and clothes are put it things should quiet down even more.
I'm still concerned about the 1/4 inch gap that I might not have left in some areas. Should I be?