Heavy Metal

Bridgestones are known for being pretty quite tire overall, but you can do better. Look at the reviews on Tirerack for noise comparisons. Dropping to a smaller rim will have no effect on noise, because as you surmised, the diameter (hence the distance from the noise source to the cabin) will remain the same. Only tread design or additional chassis sound dampening will tackle the problem. Smaller rims and taller sidewall will gain you in ride comfort at a loss of quicker steering response. Vince