So your saying the noise is the sound of the PWM activating as the mosfet is switching/ filtering the current and or voltage? The noise kind of sounds like a capacitor (a mosfet can sometimes be a capacitor?) which as you will know can store a charge during the AC wavelength when unused then use the stored power when the sine wave supplies less than your appliances prescribed voltage.The sound isn't made by the MOSFETs. It's caused by the switching of the MOSFETs and the sound is the current pulsing through the magnetics (probably the inductor coil). They probably covered a bunch of components with caulk and it's fallen off or dried up or something.
This brings me to my above post about some electrical work being carried out and the issues OP is facing. If the power supplying the PC is poor ie earth leakage or lack of earthing then maybe that could cause the components in the psu to struggle maybe causing the noise? And if this is the case the psu could potentially fail and take other parts in the PC out with it. I could be over exaggerating usually its poor electrical devices that trip the circuit protection before an issue can occur. But since im from new zealand and have no idea which country OP is from it could be possible. I have heard the states do have issues with their power delivery thats why alot of you folks have UPS protecting your PC's etc
I work as an electrician for an HVAC company I dont know alot about PCB's and their components. But a work colleague is a registered service technician so its quite good when we both go out to call outs together.
He knows the nitty gritty and i know the power delivery! Means we both get to learn!
Hope what I said wasnt completely wrong im still learning the component ins and outs