I am using a NOS AT PSU in a new build, and I am having intermittent troubles with it. I know there are some people here who are very good at dealing with PSUs, so I was hoping someone could help.

The issue happens intermittently, most often after I open the case to tinker with its innards but very rarely after long times of inactivity as well. Upon start, the lights and fans spin for only a moment, after which there is only a strange sound coming from the PSU that resembles a relay that keeps continuously and very rapidly switching, kind of like a "Trrrrrrrrrrrrrrrrrrrrrr" if you will. When I take a multimeter to the system at this point I find that there is 2.3V on the 12V rail and 1V on the 5V rail, i.e. 1/5th the normal levels on both. Testing for continuity finds very little resistance between 12V and G (0.0064 Ohms) and results in a beep but I believe this is erroneous and unrelated. Regardless, if I keep unplugging/plugging molex connectors and poking around into them, after turning the system on and off a few times (varying between 2 to a few dozen attempts) it starts working fine and works fine for a long time, even between cold boots. There is no single molex I can identify that tinkering with is particularly helpful.

I can not say with certainty but I have a feeling this issue has to do with the case being physically moved so I suppose something may be causing a short somewhere, possibly on the motherboard, but I can not figure out what or how. Another possibility is that something is wrong inside the PSU. What steps do you propose to take in troubleshooting this hard to replicate problem? If there are any particular photos you would need, let me know and I will take them.