[SOLVED] PSU Makes faint high pitched sound even when off

Solution
It is 650W so it is more than enough voltage

Thanks

650W is wattage. Not voltage.

If it's a fairly modern PSU, it would have to meet standby efficiency requirements. This requires some designs to use switching frequencies within an audible frequency. So it's not uncommon.
No. It's not normal.

It's most likely being produced by the PSU's standby circuit. If you turn off the PSU's AC power switch or unplug the PSU from the AC power socket and the sound disappears then that would confirm that it is being produced by the PSU's standby circuit.