I have two Superba 1s - one alto and one tenor.
I'll say up front that I've played sax for about 25 years - I'm a decent player and I have pretty good pitch.
I find that my upper (not altissimo) G and A seem to have a strong undertone - the octave below.
I can lip around it with some...
So i've been experiencing some strange "undertones" (or I guess that's what you would call them) on my Alto. I recently picked up a chu berry from 26, and I absolutely love it. I'm a tenor player mainly, but I've been working out my alto intonation, long tones, overtones, etc...