Hi, I had this PSU for about 1 year not used much, but nonetheless it started to have this high pitch whine noise from PSU even when PC of off. I decided to post how I fixed the problem.
1. Coat all coils with enamel lacquer (also called nitro lacquer)
Tip. You put some small magnet on a wood stick and then when PSU is ON to each coil to find the offending coil. As this is dangerous you need to know what you are doing.
2. You can look at the electrolytic caps, as in my case 2 were bad, so after replacing them the noise went away.
Here is a photo of the bad caps.