I decided to clean out my CPU case. I've had it apart before to add and remove hardware. Anyway, I completely dis-assembled it. I took the motherboard out of the case, fans, the works.
I put everything back together and plugged the thing in. Without turning the machine on, and about a couple seconds of plugging the CPU in, the power supply makes a high pitched noise. I immediately unplug the CPU, the high pitch noise continues for a couple of seconds, making me think it's a capacitor.
Anyhow, I have unplugged all of the components except the power supply. So, it's just the power supply, nothing hooked up to it. The squeal still persists.
Anyway, this sound was not there before I took the computer apart. What did I do to mess it up? All I did was vacuum the case out.
I think you need to be more precise in language to get good help.
By CPU, do you mean Motherboard?
The CPU is a chip that fits on a socket on the motherboard.
Don’t ever plug in the PSU while you are working on the computer.
The PSU should not turn on without motherboard connected. The on off switch is on the case and connected to the motherboard. If you could give a more accurate account of the situation you will get more help.