Grant,

sorry your having sound/drone problems, unfortunately sound has a tendancy to react differently to length size and volume and can change from car to car.

A resonated tip should get rid of the drone for you.

6 to 8 inches of perferation of the same size as the tailpipe should do the trick. If you go bigger, chances are you will aggravate the problem and much smaller seems to produce a sound similar to a cornered cat.

John