hi,
could that be when you start the machine this the gate selector switch, set to Hold position?
If so, the gate could be opened, and by default the VCO start at the lowest possible frequency (CV =0V), so around 16Hz. At this frequency your speakers could be wobbling indeed. Depending on the harmonic content of the waveforms mixer settings, specially if using metalizer or rich high order harmonics generator, you could get high freq sounds on top.