Continuous sound from CPU?

Actually i have unplugged all my system wires to clean the dusts in my computer...but after i connect all the wires it is working properly...but whn i on the cpu it makes continuous sound...i have checked all the wires and i have connected correctly...but the sound is the problem...pls help me in resolving this...what is the reason behind and wat should i do to solve ths problm??? thanks in advance