I have a three phase MP2 5000/48 setup configured as EES. Grid is connected to AC-IN, all loads are in parallel as well as a Fronius Inverter GEN24. Installation in Germany with German Grid code.
The system works since over one year without flaw. It still does, BUT last night at 4am it produced a new sound, which sounds not healthy. The whole setup also vibrates and even without active pulling/pushing power (<100W) the fan on one of the MP2 is turning on. The sound is generated in one of the MP2 and travels from one to another. So it cycles the whole time. The setup was not changed, there was no failure and apart from this new sound everything works like it should.
Today, while the PV was producing a lot of power and the battery got charged, the pulsation was nearly unnoticeable.
If the grid connection on AC-In is cut, the system switches to off-grid mode and the humming is gone instantly. I will change the setup to off-grid config, disconnect the grid and connect all loads to AC-Out 1 and see if that helps. But this is not feasible in the winter time with little PV incoming.
Attached you can hear a video.