Here is the update from Doug - would have been good to know this
before I installed.
Yes I see the problem. You tightened the bolt to tight. This is a common mistake my customers make. When you tighten the bolt you just compress the lock washer and go 1/4 turn more. And no more you can use a little lock tight if you are concerned about the nut backing off. If you tighten them to tight that is what happens. In the rubber about 3/8 of an inch from the end. There is a disk and the stud is attached to the disk. Same on other side. This is why the vibrations are not transmuted to the car. And why it is easy to pull them apart.