Leaving aside the crazy hypothesis coming from nowhere about sound transmission, what can probably be done is hiding a persistent malware in a microcontroler co

Leaving aside the crazy hypothesis coming from nowhere about sound transmission, what can probably be done is hiding a persistent malware in a microcontroler connected to the smbus. Very hard to detect, most (all?) modern motherboards already have at least one, FW distinct from the bios, might not be even readable without a dedicated hardware programmer and custom wiring (even in this case the FW might be locked down), and probably can own the whole system. IIRC the smbus goes pretty much everywhere in a modern computer.