I bought a set of Prothane 19mm rear sway bar bushings and just installed them. No noise at all, zero, not a peep. Could aftermarket polyurethane bushings be the definate answer? We will see with time. By the way, the Prothane 12-1105 bushing kit is only listed for the Mazda3 but it does fit the Mazda5 sway bar. Note: the bushings are bigger then the OEM bushings, so you will have to also buy the rear sway bar bushing U-brackets from a 2012 and newer Mazda5 so that they fit. I already had these brackets since I had upgraded to the newer bushings as well so it worked out nicely. Also, you will have to cut and remove the small rubber band that is held in place by an aluminum metal band that acts as a stopper for the OEM bushings in order for the Prothane bushings to fit. It's a very easy upgrade that took 20 mins to do. I will report back as time goes by.