I have a Masahiro Cherry Blossom. After a little while of use, I noticed the tsuba was becoming loose. It wasn't terrible loose, but it did rattle when it struck the intended target.
In order to fix it, I simply took a piece or corrugated cardboard and cut out the proper size, then cut it in half to make it a tid bit thinner. Problem solved. It's been months since I've done it, and it worked great.