[gliding_serpent]

I think it depends on the definition of drone. The common thought is that what many refer to as drone is from pulsations between two pipes of a dual exhaust.
It is thus felt that all single-out mufflers have no drone. In our cars this tends to occur between 2-3K rpm and is a low to medium frequency. My dansk sport dual out has it most notably between 2rpm and 2500rpm, tapering off as you hit 3K. I keep cruising at 3K or above and it is a non-issue.

But drone to others is just a frequency of noise that is annoying and more notable at a certain rpm (cruising is the one that gets most people, to a lesser degree idle). I suppose many mufflers can meet that criterion to someone out there. Others might describe it as booming, most of us get upset when a muffler is simply too loud.