Cluster synth engine - artefact after attack

Take, for example the cluster synth “caterpillar” patch. Sequence it to play just a note on the first beat of each bar (using either pattern or endless sequencer). Set the sequencer running.

There seems to be a second (smaller) attack after each main attack.

This is also apparent even with FX and LFO turned off. And it’s apparent on other cluster synth patches such as “serious bass”.

Am I going mad or is there a reasonable explanation?