AX760 High Pitch Hiss

I recently purchased a AX760 for my new computer build. I noticed that after I shutdown the computer a high pitch hiss emanates from the PSU. If I switch the power supply off then back on it no longer hisses. I've checked for the sound while the computer is running and it doesn't seem present. My system is quite silent so I'm fairly certain I'd hear it. I've tried switching outlets, surge protectors, using no surge protector, but the sound is always present after I shutdown the machine.

I'm quite familiar with coil whine. I recently RMA'd a Seasonic x-760 from another system that made awful noises unless I disabled C1E, which in my opinion, is not a solution. Beside, the sound was still present at times, just not nearly as bad. Anyway, given my experience with Seasonic PSU, which to my understanding, is what my new AX760 is built with, I was hesitant about buying one. While I'm not experiencing the terrible whine that plagued my x-760, I'd like to get to the bottom of the AX760 hiss.

Edit: I should add that before my AX760 arrived, I used a PC Power & Cooling 760 Silencer, which didn't have a single issue in my new setup. I didn't want to use is permanently though, because it didn't mount quite right in my case and wasn't modular.

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