Okay, I know it sounds crazy, but the first few times I heard the sound when taking off I seriously thought the centerstand had been left partially down and it sprung up to the frame. This is my first K-bike (and first BMW), so this may be normal and I'm just not accustomed to it. I can actually "feel" something as well as hear the sound, and my years of wrenching on other bikes is sending a "red flag" up telling me to check things out before they become worse.
Any input on what the sound could be? Again, just as the clutch engages. I also hear a similar sound when downshifting into first (but not other gears). 1996 K1100RS, 77K miles, well maintained, all splines last done around 50K.