On Sun, 12 Jul 2015 10:24:07 -0700, Gunner Asch
wrote:

On Thu, 9 Jul 2015 04:15:43 -0700 (PDT), robobass
wrote:

Trying to think of another way to measure, I attached a small 220v axial fan to the inverter. The pitch of the fan was about a major third higher than when run on the mains, meaning about 25% higher.

Bad inverter then.
A square wave will make an insuction motor "sing" differently than a
sine wave of the same eddectivr amplitude.