Case makes strange rattling noise

So many computer makes this weird sputtering/rattling noise and I just can't seem the figure out where it is.

1) It sounds like a fan hitting against something (sort of). It sometimes goes away, then comes back. It changes speed sometimes too.
2) There's no wires obstructing the fans
3) It sounds like its coming from the PSU/CPU fan (they're right next to one another)
4) It goes away if I put my tower on its side.

Does anyone have any ideas or tips? Is there a chance it could be coming from inside the PSU? I've also tried screwing everything on tighter to eliminate any rattling but it doesnt help. I'm desperate here

Ok, I figured out it was coming from the PSU fan. i have a coolermaster 650W PSU. any suggestions?

I don't think so. When I stop the PSU fan with a pen the noise stops. Also pressing on the side paneling or the outside of the PSU or anything doesn't change the noise at all.

Probably a wire touching the fan,if it is under warranty and you do not care, and know how to open it up, it is really easy to fix,otherwise it will be a big hassle and may include shipping charges,just to quiet a wire..you could take the psu out of your case and with a flashlight try to see it you can get at it with a long pipe cleaner...