At darn near precicely 4000rpm, the spring (heavy Eibach) on the rear shock resonates with a wicked vibration, I swear I can hear and feel it thrum, if touched at 4k it's impossible to hold a finger to. The juducious application of throttle (up/down) can make the spring ramp up and down like a guitar string? This vibration ends up at the footpegs (3 sets) bars (1 set), and my butt. Being a big single vibration is a given, should this vibration concern me re: engine longevity, or is it just the nature of this beast just carry on, ans ay thanks for the massage. In diagnosing the vibration (over 3100k and several days) the engine seems pretty much vibration free, or at least as free as 648cc of kLr can be and the vibration certainly mellows some once well past 4k rpm. What do you think, should I just try to enjoy the buzz, or is this something bigger?