When I run the synth in Mu.Lab when playback starts and there is a note at that point it just plays a popping noise. All the subsequent notes play back ok.
I'm testing this with the latest Mu.Lab M3 beta which can be downloaded from
If you haven't used Mu.Lab it's quite easy to test as it does not need installing - just unpack the zip and run it.
The developers email address is on this page
Hope this can be sorted.