It's the LCA creaking. Most of the time you won't be able to reproduce any noises by shaking the suspension yourself, because you can't duplicate the forces put on the parts by the weight of the car and going over bumps can. My car was making every noise in the book (bumping, creaking, groaning and squeaking). It had 145K on it, and everything was original and shot. BTW, raising the car and shaking things was a waste of time, since it wouldn't make any of those noises for me.
Rebuilding the entire suspension took care of all the noises.
How many miles on your car? If it's over 80K it's probably due for new LCAs, not to mention drop links and trailing arms. At that point, since you have to have it all apart, you may as well replace the shocks and all the other bushings as well.
Welcome to Porsche ownership!
