Crackling noise on ALL of my PSU's

Hello,

I'm currently at my third PSU. My first one was a CS750M. Had it for 4 years until it died this year. Before it died it was generating an electrical crackling/frying noise. This was going on for at least months. I don't know if the PSU died because of this or because of something else. We did have a fuse blown at our house at that moment, but I use an UPS with surge protection, so that was very weird (unless the surge protection only works from external surges and not issues from within your pc?).

I replaced the CS750M with a TX650M in June this year. This one was running fine until 1 or 2 weeks ago it also started making this crackling noise when the system is under load. I didn't hesitate and RMA'd my PSU to my local supplier and received a new one (TX650M as well). I just assumed this was a coincidence.

Guess what happened when I installed my new one this week? Yep.. the same thing. It generates the same noise when under load. On idle it works just fine, just like the second PSU. 3 different PSU's, three times the crackling noise. I made a video so you can hear the sound: [ame=

The noise can be heard from the upper right corner of the PSU when you view the pc from behind, knowing the PSU is installed with the fan aimed downwards.

I already did some troubleshooting without any result:

1. Before I installed my new PSU I cleaned my case, so dust is not and wasn't the issue.
   
2. When I powered the pc on, I only had the mobo & the cpu power cable connected. GPU, HDD's etc were not connected to the PSU yet. I could hear the crackling noise immediately upon startup, albeit not as loud. I also replaced the previous external cable with the new one. So this can't be related with my power cables.
   
3. As mentioned before, my PC is attached to a UPS with battery & surge protection. I thought it might be related to this so I plugged the power cable directly in the wall socket. Even tried multiple sockets. The issue persists.
   
4. I undid the overclock on my system and booted with a default profile, still crackles under load.
   
5. Did a stress test with Aida64. First only on the cpu, fpu, cache & ram. No crackling heard. But when I stresstest including the gpu or only with the gpu the crackling is there again. (kinda normal, gpu = biggest power user)

I'm out of ideas. Either this is a motherboard related issue (Asus Maximus VI Hero) or the power at my house is not good? I could REALLY use some help here please. My local pc guy asked around to some of his suppliers, they don't know a possible reason as well.

Thank you.