Set filter resonance all the way up and use an LFO to modulate the cutoff.
The 2500 doesn't have a dedicated LFO, but the 1023 VCO module has a slow range
which does a fine job here.... though a separate LFO would be useful.
I'm also using an envelope and some random voltages to modulate the LFO speed.
You could also just turn the LFO speed knob by hand.