This patch is simple but requires filter tweaking to get just right. Try this:
Oscillator: Two oscillators, both squares waves, one octave apart. Make the lower one slightly quieter than the upper one.
Filter: Low pass, 24 dB. Turn the cutoff way down so it’s almost a sub bass. Then boost the res a bit. Modulate the cutoff with…
Filter Envelope: Sustain at 0, with a medium Decay around 800 ms. And then just enough envelope amount to make it go “eeow”. Then, you’ll have to tweak the Cutoff, Res, and Envelope amount until it sounds just right.