Steve,
I get a little flicker (some varying brightness) on the 120V lights that are on dimmers especially. The panel holds 119 to 120V with light to moderate loads so I think the dimmers do not love the generator waveforms. They usually work by wave chopping. You can plug in a lamp with no dimmer and see if that is fine, if so it is the dimmer and not anything to worry about.
Later Ed