I've developed that "known" engine rattle noise on my 2000 softail (carbureted), but I didn't notice it until I switched to synthetic oil during the last servicing. Anyone else experience this? The stage 3 upgrade thread says Harley's rattle after they get hot because of the rods and lifters getting hot and expanding. Is synthetic oil increasing the internal temp? What's going on? While riding, the rhythmic rattling noise is about as loud as the exhaust at 55 mph.