Make a MIDI clip with some notes so that it will glide to one octave lower after 1/16 (for example 1/8 G#2 note befor 1/8 G#1 note which is 1/16 afterwards)
Oscillator:
Saw D wave and envelope goes from 0dB to -inF in decay in 1-1.5s
Filter:
LP 24dB with similar envelope (doesn't have to be the same)
freq: somewhere in 100-300Hz
Q: 1-3
Envelope: 20-40%
Put also the Voices to 1 and set glide on with 50ms
Saturator:
Soft Sine with 15-20dB drive.
dry/wet 50%
I like to use the color option to cut some saturation on the lower frequencies (base -10, freq 350, width 35%)
Experiment with filter envelope decay time, freq, q and envelope and saturator drive
Now you are ready to creak with acid
I have never used a 303 (and not any "real" emulator also) so i cant say how accurate this is. Improvement suggestions are welcome!