Fix My Squeaking Floor
If you live in a 2-story house, you probably have a squeaking floor somewhere. This isn't fun to contend with, especially if your spouse is now asleep and you want him/her to stay that way. You need to either fix the squeak or develop skills like a gazelle to bound over it.
Typically, the squeaking noise can be traced to the sub flooring riding up and down on the shank of a nail. As you put your weight on the floor, the wood sub-floor travels down and squeaks. As you lift your foot and remove your weight from the area, the floor rides back up on the nail and squeaks some more.
You have a couple of options here. If you are going to replace the carpeting anyway, you can pull up the carpet from the area and screw a couple of deck screws into the sub floor. This will pin it to the joists and eliminate the movement. This is the safest way.
If you aren't planning on replacing the carpeting, you can either hire someone to stretch and re-secure the carpet back down after you fix the noise. Or, if you like some risk, you can get a nail gun and shoot a couple long nails at opposing angles through the sub floor and into the joist. You better hope there isn't a water line lurking close by though.
If you have vinyl flooring, you will likely have to get access via the ceiling of the first floor as you can‘t peel back the vinyl and reinstall it. You will probably need to cut a hole in the ceiling below and shim and glue to fill the gap and stop the movement. Then you have to repair the ceiling.