Lynn, Tracy, et all,
The idea is to change the resonant frequency of the bolt and just the heat shrink would do that. Contact with the intermediate hsg. would do it better.
Here is an idea, would it be possible to drill a small hole near the center of the bolt hole path from outside the housing and INJECT some RTV Silicone? A very small hole less than 1/8" would do it. The bolt would then be positively captured. Just thinking out loud.
Bill Jepson