D3 generates harmonic at D5?

Pianoteq 9 Standard question. I am noting a sinusoidal tone at D5 when I press D3 (D above Middle C on my controller) perhaps 9 dB down, in Steinway American D and other grand piano models. The tone largely vanishes on adjacent and other pitches, e.g. C#3 and D#3. This is with only D3 pressed and held, no pedals or apparent sympathetic resonance active.

In another forum three years ago, someone noted this D3/D5 behavior, but it was written off at the time as normal because commenters assumed he was pressing multiple notes with the pedal down. It is possible he was hearing what I'm describing.

Has anyone else heard this, or can someone test to see if it is reproducible? It's not a huge issue, just a minor annoyance. In production I would add a dynamic notch filter at D5 on the piano track to control this a bit. Thanks much.

Update: The sine tone is affected by the 4th harmonic setting in Spectrum Profile. With "4" set to 0, the tone is audible at D3 (D above middle C) but not other pitches. When I max "4", each played note generates its sinusoid two octaves up, with D3 still most affected. When I reduce "4", the D3 issue reduces as expected, with some subtle effect on other pitches. If I update to Pianoteq 9 Pro, I'll be able to reduce Spectrum Profile "4" say by -7dB on just the D3 note.