update: reap top node: I've copied this reply to the original node.

Why and what are you printing to SOXOUT? IOW why are you printing anything to SOXOUT and extrapolating from that why are you using open2 at all?

Removing the print SOXOUT $buf; line seems to fix the issue as far as I'm able to reproduce it.

As far as I can see it looks like you're misunderstanding the sox interface.