I've noticed this behavior on two of my cats, and I don't believe it is feline hyperesthesia (neither exhibit any of the other symptoms commonly associated with the condition, and the back twitching does not seem random).
Instead, I believe it is possibly a social/communication cue of some sort.
Typically, it seems that the two cats (our oldest, an alpha female, and our younger male) both will display the back-twitching behavior when I start talking to them.
What does this mean? Is it an invitation to pet them (both are quite affectionate)? Is there documented research that describes this behavior as a social cue among cats?