I have never had a problem with any of the BVM Smooth stops that i have. If you are hearing a Hiss pull the plunger out and make sure that you did not plug the hole on the end with O-ring lube if you relubed the O-ring before you installed it.

Also you have to make sure that the linkage is running in a straight line with out any binding on the plunger during the movement of the servo and plunger.