Noise coming from computer

Hi there, I found this forum and was wondering if you could help.

I built my PC around a year ago and over the last 4 months it has been making an annoying ringing noise whenever it is on, I have to flip the switch on the back of the power supply to stop it, this made me think I need a new power supply but then I have noticed that sometimes when I plug my headphone or mic into the front jacks or pull one out the noise stops instantly so I was thinking it could be something to do with the wireing in the case.

Would be great if anyone knows the answer, its doing mu head in haha

If you need to know anything about the pc feel free to ask

The only times I think that I have ever heard of that involved ringing sounds were either bad PSUs or bad motherboards.

Please tell me what all your specs are, be sure to include your case maker/model, your PSU maker/model, and your motherboard maker/model. Everything else would be nice too.

Also, does that ringing stay gone when you unplug the headphones or does it start up again after a short time off?