That's why I like to leave my sub in standby also. I get that "THUNK" that you describe, although it certainly isn't loud, it doesn't sound healthy. On second thought , it probably would be load if my receiver volume was turned up but I have a habit of always turning my receiver all the way down when not in use.
Anyway, that's one reason I wouldn't buy the Klipsch, you never know if the standby mode is going to work or not. I don't care how much energy it uses in the on position or the standby position and I understand some folks who say it doesn't bother them if it works or not. When I buy something I want it to work like it's suppose to work and it's that simple.