"i also know that its not the fan in the psu cause it does not make the noise when its off and the fan is not moving'
No noise when the fan is not running, and from that you conclude the fan is not the noise source?
The fan may well be the problem. One way to test, stupid as this sounds, is to stop the fan briefly while it is running. If you can see / reach the fan while the system is running normally, just stick a rod (Screwdriver?) into the fan for a moment to stop it, but only keep it stopped for a few seconds. When you pull out the rod, make sure the fan starts up again immediately. If it does not, shut your system down right away. If the noise stops when the fan is stalled, you have the source nailed down.
If this does not stop the noise, and you're still sure the noise comes from the PSU and not somewhere else, your best bet is to replace the PSU. It may have electronic components making that sound and trying to find and replace them is not worth the time, trouble and cost.
If the fan is the noise source, you have three options. Obviously one is to replace the PSU. Another is to disconnect the power supply completely, take the PSU out, open its case, use a wire to ground out everything inside to its outer case, then remove the fan and try to find a replacement that will fit. The third option, once you have it out, is to oil it. Most have some sort of adhesive label cover on the hub of the fan. You can lift it carefully and stick it back down afterward. Get a small bottle of a light oil, like sewing machine oil, and put a tiny amount (no more than 2 drops) on the bearing or the shaft next to the bearing. Turn the fan by hand a bit to help the oil flow in, then re-assemble and see if that helps. It will not be a permanent fix, so you may have to do it again in a while. In the meantime, look for a replacement unit.