Unknown High Frequency Distortion, Recording or Speaker?

I just upgraded to Audioengine's HD6 power speaker, from the much smaller A2+. My expectation was that since the drivers are bigger and not only with far more power, but dual amps, that it would produce better mid-range and have more detailed treble. In many ways it has...but I am noticeing a weird high frequency grain-like distortion.  Like something is vibrating at a high frequency, smearing the details. Thus far, I have only heard it on two songs that I test with:

Billy Joel's "New York State of Mind."  In this song, the piano is fine, but when he sings, it's as if he is singing through an old paper cone and the paper is vibrating, causing a grainy sound to his voice.

Journey's "Faithfully" the piano distorts in the high freqncy range, as though it was recorded beyond the 0 db range and distorting, but when Steve sings...it's fine. *shrug.*

But here's the kicker.  When I run sine waves, no issue. It will start from 20hz and cycle all the way up to 20Khz with zero distorition.

Also, the A2+ did not have these issues and the HD6 is using the exact same cables and power back end. The only thing that has changed, other than the speaker itself, are the stands.  The A2+ was on the desk with their rubber stands.  The HD6 are on metal Sanus 30" speaker stands and on spikes.

So, the question is...is there something in my system causing the distortion or is it just the recording and I never noticed because I didn't have as high a resolving speaker?