What exactly is drone?

 

Essentially it's exhaust resonance that occurs are varying rpms. Typically in overdrive... Some are more tolerant than others. Stealth tubes can mathematically kill the resonance

 

It's like when you're cruising and the exhaust tone is constant and really annoying. If the muffler's "sweet spot" (loud point) is at 2000 RPM and that's the RPM you're sitting at indefinitely, it'll make drone. At least that how I understand it and how my exhaust and drone seem to work