Let’s figure out where the noise is coming from. On the C16 and any other 264 series machine the TED chip does audio, video and I/O. Pin 33 on the chip is the sound output it seems. During a directory listing this stays flat on the scope. When I run a game we can see the waveform. So this rules out the TED chip I would say.
#commdore #c16 #plus4
@root42 3Vpp doesn't look like it's induced by accident, and 50% duty cycle looks like a clock signal 🤔
@lasse now that you mention it: looks indeed suspicious. The audio waveform should look a bit different.