In my car, I run mobil1 full synthetic euro formula 5-40. If tried a few other brands and IMO, mobil1 seems to make my car run the smoothest. As for your clunking sound, I wanna say that there's little clips that fit on the end of the pads to make them fit snug in the caliper. When I did my brakes, the pad supplier put those in the box. Didn't have to use them cause every thing fit pretty snug.