[A6] artefact noise with PWM waveforms

[Eric]

I'm a new owner of an A6 and I encouter a problem with PWM waveforms.
Wether I use VCO 1 or 2, there is a backing distorded noise almost at
"constant pitch" generated with the PWM waveform (Square Waveform + PWM
Led on)  that I can easily ear above C3 on all programs that use PWM. I
did the autotune trick several times and everything shows OK. I started
some programming from scratch but got still the noise. So what's wrong
with the PWM waveforms ? Do you get the same thing than I ?