clearly some experience needs to be shed on this issue. one word = fire.
if your PSU is 'squealing' its because it's capacitors are doing it because they are blown or corroding significantly, or electricity is arcing on the inside of the PSU. neither is good. if left untreated, you could be looking at something as small as a new PSU, or you could have to replace most components in the PC if they get blown out by a short in the PSU, or your PC could just ignite into flames from electrical arcs and dust and burn down your house...
sounds far-fetched doesn't it? yes, well, it's not. so toss your cheap chinese power supply and go spend your $20-30 on a new one from the store. my experience comes with advice -- don't wait until you start to hear the noise again, replace it now.
on a side note, if you're not sure it was the PSU making the noise, inspect your mobo's capacitors as well. if they are not flat on top, bulging out, showing signs of 'leaking' or corrosion/oxidation, then they are bad and potential candidates for your strange noise. check them all -- if they look fine, its your PSU.