Here’s the song:
The sound in question is clearly heard at around :03 seconds. It plays the same note until around 0:30 seconds when it starts playing two notes.
And you can hear it at 0:18 seconds into this version:
I’m also interested in the bass sound that starts at 0:22 seconds and continues at 0:40 seconds.
I’ve tried to make similar patches but can’t really get close. The first sound is definitely modulated somehow, there’s slight delay and possibly chorus. I don’t know if they’re pulse or square waves with PWM, or saws, or what exactly is being modulated. Cut-off? PWM?
The second sound, the bass, sounds simpler, but I still can’t get it. It seems to have some cut-off modulation, but that’s about all I can guess.