i've contacted a few that have the noise and were 550's and non xdrive as well.
Like i said the springs are awesome and adding a rubber hose into the top two coils eliminates all possibilities for any noise. Could be installer error or could be just manufacturing differences. Could also be some people are more sensitive to noise than others. Its not loud but if you have the radio off you can hear it over certain light bumps. Personally i doubt so many installers made the same error so i think its the springs. I would add the rubber sleeve even if they didn't make noise since that only helps prevent noise in the long run.