1) make sure there are no wires in the way of the fan
2) make sure fans are spinning, other wise turn the computer off or you can damage things
3) screeching noises are pretty easy to find their location, open the case up and turn it on while at a bench. touch (don't press hard!) the fans, and when one stops and the whine stops then you know you found the bad fan. RMA the part if it is under warranty. If the CPU fan is not under warranty (it should be), then replace it with an 1155 cooler like the hyper 212+ (or something smaller if that is too large for your case).
If you have an OCZ PSU then no surprise. You need to locate the noise. You can use a piece of paper in a small funnel and listen. Some HSF can also do this so listen around the PSU and CPU areas first.