Answer to "Macintosh SE hisses/whistles when turned on. No video"For the video, it looks as if the board on the back of the CRT is a little loose in the picture. This sometimes happens during transport, all you need to do is push it in, and then it should be fine. It should be safe to do so, as long as you don’t touch any other part of the CRT. Also, adjust the brightness (under the Apple logo) if needed. As for the noise, that’s your fan. I wish I had a better solution beyond replacement, but I have the same problem on my SE, and have yet to find an alternative. I tried cleaning out the accumulated dust several times over the decades, but it made no difference. My guess is that the motor is either gummed up with dirt, or just wearing out. The good news is that, while it sounds horrible, it’s really not a danger to your machine, and last I checked, suitable replacements are still available.