You can set the ramp rate. But you need to get into the “profi” menu, and for that you need an unlock code from Fronius, which requires signing paperwork… and may affect the warranty even. Not entirely sure. The code is forever, you can always reuse it, but it works only for your unit. Tied to the serial number.
So it turns out I was (am?) an idiot…
The Fronius wasn’t set to MG50 country code, because I factory reset it afterwards to access the Modbus control settings and didn’t set MG50 again. 
Works great now, thanks @Sarel.Wagner!
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So what have you implemented as your long term solution?
I also recently bought a 10kVA Multi and it feels much nosier than my 3kVA MPII.
Mine is installed in the pantry adjacent to the kitchen, and the kitchen is adjacent to my living room 
I have actually managed to soothe the savage beast, will take some pictures and post.
First thing to check is your serial number. If it’s after this, thank Lord Vader that your problem isn’t worse (mine is earlier).
The electronics design in the MP-IIs has been improved to run the fan better and have it make less noise.
The control, and thus the noise, is improved for all speeds except full speed. In other words, at 100% fan speed, there is no difference between the old and the new models.
Sadly it seems like I also have a old model (SN: HQ2146)
So I am very interested to see what you implemented 
Haven’t forgot about you, here’s something in the meantime:
Retrofit kit available*!
2023-02 - MPII Retrofit kit to reduce low RPM fan noise v1.pdf (365.1 KB)
*For certain interpretations of available.
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