pHAT Beat strangeness - sparks?

I’m currently refurbishing and Pi-ifying a vintage (okay, 90s isn’t vintage…) radio. I’m hoping to use the pHAT Beat from a Zero Pirate Radio Kit for the electronic guts of it.

However, I’m having a strange issue. When I first booted it up, I saw a spark coming from the pHAT itself. Now, whenever pulseaudio is enabled or disabled, I get an electrical spark noise and the bare wires to the speakers “flicker” and occasionally there’s a spark.

Any idea what could be wrong?

I’ve used both a Pi 4 and a Zero to try this - so I know it’s not the Pi.
The speakers are 4 ohms, 3 watt. These ones:

Hope someone can help :-)