Windows 7: PSU making noise!

My PSU just started making a noise, like if something's touching the fan. It's a different computer from the one in my specs. It's a sturdy black one, however this PC has no case and the PSU is positioned in a way that the fan is on top and sucks in air, so a lot of dust goes in. Since September it was this way. But a minute ago it's making this loud noise, though nothing's touching the fan. Should I turn off my computer or not. I'm doing a LOT of stuff right now. Once my house doesn't burn. PS. I only restart my computer after 3 months when I need to reinstall Vista - yes I could activate it however it's a reminder Windows got bloated over the period of time.

Hi StackOverflow,

I would shutdown the computer and take the PSU out and use canned air to blow out anything that may be in the PSU with the fan facing downwards. Hopefully that will end the noise. If not, the PSU fan may be going out on it.

That means I gotta take off the computer. OK, bye.