@macclassic I agree with
@Johnnya101, that sounds like your power supply is dropping out. Specifically, for me, that T shaped flash you are seeing. The sound almost identical to the flash you would see if the machine was running and you suddenly yanked out the power cable.
Additionally, the raspberry (I’m assuming fart) sound emitted from the speaker at the same time could be from the power dropping off at the logic board not quite instantly, but near instant (say a span of 100 milliseconds).
The fan will continue to spin until the voltages coming off the PSU get really low, with just some gradual loss of RPM on the way down. So if your PSU is dropping the 12/5 volt rails suddenly to 8 or 9 and 3 volts, I’d expect most of what you are describing, but the fan to keep going at a decent pace.
Luckily, the SE/30 has an external floppy disk port. That is probably the easiest place to monitor the voltages from. There are several mappings around the internet that describe which pins are the ground, +5, +12, and -12.
Likely the capacitors, though there are also some potentiometers to manually adjust the voltage by some weird ratio. Yours may just be shorting out in relation to how much amperage is being loaded onto the PSU (so less ram, less power needed, longer time before short causing voltage drop off???) at any rate, start with a voltmeter and track your PSU. You don’t even need to open the case for that.
Good luck!
I'm going to check the card on on the yoke and it's pins for signs of arcing too.
