Someone called this morning to relay the news that my cluster was making a horrible, high-pitched noise that you could hear outside of the machine room. Not good. I rushed over and we discovered the PDU (power distribution unit- the thing powers all the computers) was making a screeching alarm noise. What was worse was that in its failed state, it was rapidly turning every single computer's power off and then back on again. Each of the 42 plugs made a clicking noise as it toggled, so it sounded a bit like a wimpy machine gun. Turning computers on and off continuously, over night probably took a couple of years off their life.
The lesson is: never reuse other people's junk. Chances are there's a reason they're giving it to you for free. I dug up a good, unused ServerTech PDU that I'd bought for something else last year and am back up with only a few fsck panics.
Yes, I drew the awesome picture below. Someone took a video of the bad pdu freaking out, but I'm sure someone somewhere would object to me posting it.