SASLess,
The friction is needed whan the sas is on (when you are not sasless....) because the sas actuators have to push against the friction to work the servos. If you have sas on with a fully limp noodle cyclic, some portion of the sas actuator motion will feedback toward the pilot, and that motion will be lost. This makes the sas very much less effective (it throws away about 20% of the total sas motion) and it also produces a slight and objectionable stick throbbing (the only throbbing folks of your age will ever again see). We call that "stick nibble".
Pylon rock is an artifact of the Huey family, as is collective bounce, both more prevelent in some models than in others. Pylon rock is basically a matching of the looseness of the transmission structure with a natural rotor in-plane motion. The transmission makes a slight fore and aft rocking motion that the rotor feels and amplifies, a sort of "air resonance". It is a whirl mode of the rotor that pumps the structure, and it nags the 540 system especially. It is often called the 'Huey Shuffle" and has a distinct low frequency beat as it pumps the pilots fore and aft at about 3 times per second.
Loose components can help make it big enough to be objectionable, so the advice above about mounts and lift links makes sence. In the Snake, the transmission had dampers built into its aft mounts, so the rocking of the transmission was absorbed (like the lag dampers on an articulated rotor blade). Also, the sas on a cobra had an input that came from the transmission (there were electronic transducers that read the pylon rock motion, and inserted that signal into the pitch sas so the sas would wipe the motion out by rocking the cyclic to cancel it.)
Why does the Huey have pylon rock and few other machines? Because it has no lag damping at all, so there is no resistance to the whirl mode at all, and that big heavy rotor system on the high mast has a ton of inertia that makes the mode frequency so low that it is easily felt by the crew. Also, the Huey is designed to ancient, very poor structural requirements, so that transmission is held in by very little structure. This makes it rock fairly easily, on a loose mounting structure. Before all the Huey-lovers jump on me, please recall what happens in a Huey if the rotor hits something solid - i. e. which crew member gets the transmission in his lap. Modern helos have much stronger transmissions, which stay in place when the rotor has the misfortune to hit something.