My take on it is that the "glue" binding the bushing to the spring plate failed and is allowing movement creating the noise especially when the bushing is cold and stiff. Alternatively, there may have been wear in the torsion tube allowing movement of the outer part of the bushing. It is such a PITA to remove and inspect but I will likely do at least one side this winter to try to figure out whether it is the inner or outer surface of the bushing causing the noise. The only option that I can think of is replacing with a different kind of bushing or new factory spring plates unless there is another option for bonding and the problem is the inner surface.