pre-loading is simply installing the part, you did OK with the soap initially, but that stuff dries out quickly, there is special stuff, but, anyway, preloading is installing the part while jacked up, of course, but not actually
torqing the fasteners to spec until after the car has been lowered off the jacks and all of the weight is on the suspension...that allows the bushings to seat in the proper fashion. If you lock the bushing/carriers into place without the proper stress you could experience what you mention. Your new bushings are fighting to situate themselves...Leads to premature wear as well....