About 400 miles ago I replaced both my rear shock tower mounts because of the normal rattle that happens when they fail. The rattle/clunk noise went away after I replaced them. Just a couple of days ago the rattle came back and I thought I must have gotten a bad shock tower mount. So I pulled the carpet back in the trunk and the shock mount was perfectly fine. I then loosened the nuts and re-toruqued them to specs. The noise went away for two days and today it is back again. What could this be? The shock tower is not cracked and the mount was installed correctly. Any thoughts would be great! Thanks.