Misbehaving yaw damper ?
It is the second time I encountered this issue on a 320 (-200), traveling as SLF, seated in the back. About half-way into the climb to cruise a very noticeable side-to side vibration developed, with the jerks strong enough to prevent me from typing on my laptop keyboard. The frequency was around 3-4Hz, perfectly regular, unlike the irregular jerks caused by normal yaw damper action. As soon as we reached cruise, it stopped in both cases and did not appear again during the remainder of the flight. I have informed the front row, in both cases they felt nothing but agreed the symptoms sound like the yaw damper.
Can anyone with experience on the 320 shed any light on the issue ?