@whenryb How would the stiffness of those bushings cause clunking? That doesn't make sense to me TBH. The bar should be rotating smoothly within the polyurethane bushings. I've had aftermarket sway bars with polyurethane bushings on other cars without any such issue. I drove those cars in freezing weather all winter long, chasing every snowstorm.
Perhaps an end link bolt was just slightly loose, but at warmer temps it snugged up? I'm not sure that last part is realistic or not (the bolt being more snug at warmer temps). As I mentioned earlier in this thread, I had a front end chunk on this car from a really big hit (huge missing piece of road) that knocked an end link just slightly loose. I couldn't feel anything loose by hand, but the sway bar would shift under load. This was stock sway bar and stock end links.
What is extremely typical with polyurethane sway bar bushings is they need to be re-lubricated periodically. On those cars where I ran aftermarket sway bars I tried many different kinds of lube and while most of them worked, none lasted. The initial symptom of the lube wearing out was just squeaking though, not clunking.