I've been experiencing weirdness with my power supplies and BBU. Here is my setup: Two PCs running on a single BBU - a brand-new CyberPower BC1200D (1200VA) PCs are connected to the 'battery' outlets on the BBU (not the 'surge only' outlets). PSUs are of different manufacturers (Enermax 500W and Thermaltake 400W). Both PSUs are less than 6 months old. CyberPower software reports the BBU is at about 40% load when both PCs are running. The problem: both PCs' power supplies were emitting a noticable electrical buzzing sound the other night. I powered down both systems but the buzzing continued. The only way to stop it was to either unplug them outright, or flip the hard power switch on the PSU to 'off'. After about 30 min, I powered everything back on and all was well, but I'm very concerned about this problem returning. I've heard this kind of buzzing before, but it only happens when the BBU switches to battery. Even then, it is sort of alarming to hear any sort of buzzing sound coming from the PSU. However, in this case, the PSU was not in battery mode. Has anyone had any experience with this sort of thing? Any insights would be appreciated. Thanks!