I'm not quite sure if what I am hearing is an aliasing issue or an emulation of something that actually occurs on a real ARP 2600, but when I play a single oscillator (sine, square, triangle, etc.) I hear this very low in volume frequency shifting noise (approx. -66 dB RMS on a spectrum analyzer) that approaches the fundamental from both sides of the fundamental. It's much more apparent on a sine wave due to it not being masked by overtones of other oscillator types. It may even be indistinguishable on most speaker/headphones, but my AKG K812s pretty much reveal every single detail.
Here's a screen capture showing the issue in Ableton's spectrum analyzer:https://drive.google.com/open?id=0B7hnclNeu3TMelVBTEUtaFIyNEk