This is very odd; I've been running Scratch sounds for *hundreds* of hours with no problems a t all until yesterday when BOOM - or rather '?' which is the lack of boom when required. Total lock-up of the sort that I always thought was impossible on unix.
I'm pretty sure it's not a specifically Squeak/Scratch issue since the same code runs on other machines and indeed other OSs without this happening; so probably some detail of the ALSA driver for this particular hardware.
Making Smalltalk on ARM since 1986; making your Scratch better since 2012