A floor tile in my bathroom moves and crunches when I walk on it.

Wow! You don't usually hear crunching from a tile. Is this your own home or are you renting? If you are renting tell the landlord immediately. If it is your home lift a tile that is moving and see what the heck is under there. Perhaps they used some bad thin set if it's stone tiles. If it's linoleum then the glue is degraded. Either way sounds like you have a possible diy job (or landlords job) coming up. If you own it go to Youtube for help on how to! Best of luck!

Bad install! Will need to remove and reinstall. Check that the subfloor is good shape. Sounds like it may not be and caused the breakdown of the thinset.

If you have wood subfloor it might not be thick enough, thus the tile came loose and the mortar has broken up underneath the tile. You will have to carefully pry up the tile, check to see if the subflooring is thick enough so it doesn't happen again, then relay the tile (you can buy thin set mortar -- see if they carry smaller containers of premixed for an easier job). If the subflooring isn't thick enough AND you own the house, you might have to eventually tear up all of the tile. If you can't find a grout to match look for a grout colorant (available at both Lowes and Home Depot). You might have to mix several colors to match your old grout, or if the rest of the floor is secure and you can't get the grout to match, then buy the grout colorant you like and do all of the grout, than seal it with a good grout sealer. It isn't that bad a job to do unless you have lots of tile.

Kwmayfield - You may have a bad installation and floor movement. Tile will come up because of the wrong application of thin set, subfloor movement, or to much weight on a particular tile. If the whole floor needs to be remove be sure the next installation uses Ditra subfloor bonding material, this is a cushion between the subfloor (wood floor) and tile. Application or setting of the tile is the next issue, from using the correct Thinset, trowel and buttering the back of the tile for proper bonding. P.S. Ditra product can be found at Home Depot, Lowes or your Building supplier. Check out self help and D.I.Y. videos on You-Tube