I just finished building a system, but now im getting alot of noise from one of the back end of case fans,I even tried a different fan and it just sounds like its spinning way to fast but lots of noise,I have the fans plugged straight to the powersupply,not sure if that makes a difference, the fans i have, have the bigger power plugs on them also, im on a M2N-SLI ASUS motherboard,and a 500W OZC powersupply, + these fans are cheap types,and both the fans are connected to same power cord on psu,the bottom one is just fine no noise,less air but no noise. what can the problem be? Oh and when i tap the fan while its running it seems to lower the noise for a few min.