There are no decoupling capacitors in that bit of the PCB layout and you have both analog and digital grounds cross connected then to something else through the same via.
The whole thing should really be either using ground plane construction or "star point" ground for all the analog signals, with digital ground separate and only connected to the analog side at a single point, to my way of thinking.
Without seeing the full board - all layers - the stray output could even be a side effect of the 7660 oscillator.