Thanks for all the great suggestions. I ended up doing what DougE suggested and figured when the bolts dropped into the sub floor I could squirt some expanding foam down there to trap the bolts and keep them from banging around. Turns out, there is apparently some rigid insulation in the subfloor that is keeping the bolts from dropping all the way down. Win-win! However, after doing two of the bolts, I cut the carpet back to expose the other two and they are installed the opposite direction! Why would they do this? The nuts are on the bottom, and are not captive (I checked to be sure). So I guess I'll just have to grind the head off the other two bolts.
